Every Free Comic Book Day, millions of comics are given away to readers around the world. For curious new fans and seasoned collectors alike, Free Comic Book Day is a way to sample a diverse array of titles from a range of publishers. While some comic companies reprint recent highlights from their publishing line on Free Comic Book Day, others release new material to help launch upcoming titles or stories.

RELATED: FCBD: 15 Free Comic Book Day 2017 Titles You NEED To Get

Now, CBR is counting down the best original Free Comic Book Day comics ever! For this list, we'll be taking a look back through the history of Free Comic book Day at titles that contained new, previously unpublished material. We'll be ranking these titles by their overall quality as well as how well these titles served as solid entry points into their respective series.

15 BLACKEST NIGHT (2009)

Blackest Night FCBD

On 2009's Free Comic Book Day, DC Comics released "Blackest Night" #0, a prelude to the massive crossover that would dominate the next year. Over 12 pages, Geoff Johns, Ivan Reis, Oclair Albert and Rob Hunter gave readers a crash course on the recent history of the DC Universe. Both Hal Jordan's Green Lantern and Barry Allen's Flash had returned to their roles after long absences, and recognizable heroes like Batman, Aquaman, Firestorm and Martian Manhunter were all either dead or presumed dead.

Using a story-long conversation between Green Lantern and Flash, Johns parsed out this information effectively and found room for smaller character moments. While this could've been an issue filled with talking heads, the art team kept the action going and found dynamic images that keep the issue from becoming a text-heavy exposition dump. This issue also had an efficient overview of the recently-introduced color spectrum Lantern Corps though "Secret Files"-style entries, penciled by Doug Mahnke. With checklists for the recent collections and upcoming issues, this gave readers a quick way to hop into the DC Universe.

14 SPIDER-MAN (2011)

Spider-Man Spider-Woman FCBD

The first Free Comic Book Day was organized around the premiere of Sam Raimi's "Spider-Man" in 2002. Since then, Spider-Man has been a regular part of Marvel's Free Comic Book Day giveaways. In 2011, the Web-Slinger took center stage in a free issue by Dan Slott, Humberto Ramos, Carlos Cuevas and Victor Olazaba. In addition to laying the groundwork for 2011's well-received "Spider-Island" crossover, this accessible adventure emphasized Spider-Man's larger presence in the wider Marvel Universe.

Most of the issue revolved around a battle between Spider-Man and Spider-Woman, who eventually teamed up to battle the mind-controlling monkey villain Mandrill. After that, Spider-Man started training with Shang-Chi, the Master of Kung-Fu, at the urging of the new Madame Web, former Spider-Woman Julia Carpenter. The details of Peter Parker's new job as a scientist at Horizon Labs and Spider-Man's new position as a card-carrying Avenger were naturally mentioned in this well-executed team-up tale. Even though this was a fairly different status-quo for the Wall-Crawler, there were enough familiar elements to ease readers into Spider-Man's then-current adventures with a classic Marvel team-up.

13 THE WALKING DEAD (2013)

The Walking Dead Free Comic Book Day

By 2013, "The Walking Dead" was already a bona fide pop culture phenomenon. In 2013, Image Comics used their Free Comic Book Day release to capitalize on the success of the multimedia franchise. In a collection of new and relatively little-seen short stories, Robert Kirkman and Charlie Adlard explored the histories of several prominent characters.

Michonne, Tyreese, Morgan and the Governor all starred in short tales that were heart-breaking, funny, heart-warming and horrifying, respectively. While the story of how Tyreese made a hammer his zombie-killing weapon of choice was the book's only original tale, the other stories had only appeared in publications that most "Walking Dead" fans might've missed. While this might not have been the best introduction for someone completely new to the franchise, it fleshed out the back-stories of intriguing characters who had already appeared on the live-action series. Along with a comprehensive reading list in its final pages, this book was a perfect way to pique the curiosity of the TV show's viewers and turn them into comic book readers.

12 HELLBOY (2008)

Hellboy FCBD

Shortly before the release of "Hellboy II: The Golden Army," Dark Horse Comics used their 2008 Free Comic Book Day offering to showcase three tales from the world of Mike Mignola's "Hellboy." Since the Hellboy franchise already featured an emphasis on short stories, these Mignola-penned tales gave readers a representative view of what the franchise has to offer.

In the first story, "The Mole," by Mignola and Duncan Fegredo, Hellboy had a bad dream that reflected some of the themes and recent developments in the larger Hellboy saga. After that, Mignola, John Arcudi and Guy Davis offered a beautifully illustrated B.P.R.D. tale starring Johann Kraus that followed up on recent events from the ongoing adventures of the monster-hunting organization. Finally, Mignola, Joshua Dysart and Paul Azaceta told a thrilling 1930s tale about B.P.R.D. founders Prof. Trevor Bruttenholm and Dr. Howard Eaton. While this isn't necessarily the most accessible comic, it gave characters from the film starring roles with some short, exciting tales that were sure to please regular readers.

11 BOB'S BURGERS (2016)

Bobs Burgers FCBD

Free Comic Book Day has always been a great opportunity to put a highlight on humor titles that are usually lost in a superhero-dominated market. While titles like "Archie" or "Simpsons Comics" usually reprint some of their recent tales, Oni Press gave readers a new issue of "Bob's Burgers" on 2016's Free Comic Book Day. After reprinting several stories for their 2015 offering, Oni's 2016 release gave readers three new tales based on the critically-acclaimed animated series.

Each of the three Belcher kids, Tina, Louise and Gene, starred in one of the three short stories. Tina's story, by Brian Hall and Frank Forte, centered around her imagined clones forming a dance troupe. Louise's story, by Justin Hook and Ryan Mattos, found Louise leading an adventure underneath the family's restaurant. Gene's story, by Mike Olsen and Derek Schroeder, had him undergoing a werewolf-like transformation into a lounge singer. Along with some extra pin-ups, these stories worked together to give readers a good idea of the types of stories told in the ongoing "Bob's Burgers" comic book series.

10 X-MEN/RUNAWAYS (2006)

x-men runaways

On 2006's Free Comic Book Day, Marvel highlighted two teams of outcasts who protected a world that hated and feared them. In "X-Men/Runaways," by Brian K. Vaughan and Skottie Young, Marvel's merry mutants bumped heads with the Runaways, who had only debuted three years earlier. In the story, the X-Men fought the teenage team in an attempt to recruit the super-strong young mutant Molly Hayes before parting on good terms.

Despite a packed cast and abbreviated length, Vaughan's script managed to give each character a moment or two in the spotlight. Young's exaggerated, cartoony art was a perfect match for the brief but fluid action scenes. For new readers, this was a solid introduction to the Runaways, complete with a checklist of "Runaways" collected editions for further reading. For regular readers, this was an anticipated meeting between two of that era's more prominent Marvel teams. This issue also featured a charming all-ages Franklin Richards adventure from Chris Eliopoulos and Marc Sumerak.

9 MERCURY HEAT (2015)

Mercury Heat FCBD

While most Free Comic Book Day releases are targeted towards readers of all ages, Avatar Press used their 2015 giveaway to introduce a new series for mature readers. In "Mercury Heat," Kieron Gillen and Omar Francia introduced their sci-fi space police epic and its lead, Officer Luiza Bora.

Over the main 12-page story, the creative team established Luiza's origin and explored a violent world that's protected by the Mercury Heat police force. Despite its short length, the story parsed out information well, established an intriguing world, and fit in some intense graphic action. After that, the rest of the issue featured a lengthy text piece from Gillen that offered an illuminating look behind the scenes at the development of the series. Along with commentary on Francia's sketches, Gillen openly named the series' influences and even provided a link to his writing playlist. This was an interesting pitch to an informed reader that effectively sold its creators as much as the actual series.

8 STAR WARS (2013)

Star Wars' Darth Vader wielding his lightsaber and Boba Fett aiming his blaster.

For fans of the film franchise, the expanded universe of "Star Wars" comics, novels, games and shows can be daunting. With so many original characters and stories from every era of the franchise, casual fans of the films could have a hard time find an entry point into the ongoing adventures of a galaxy far, far away. With their 2013 Free Comic Book Day release, Dark Horse Comics offered an accessible starting point with "The Assassination of Darth Vader," by Brian Wood and Ryan Odagawa.

In that short story, Darth Vader and Boba Fett fought off an assassination attempt by the Imperial Captain Torn and his squad of Stormtroopers. With exciting moments like Vader crushing a Tie Fighter with the Force, this story showed why he and Fett were some of the most feared characters in the "Star Wars" Universe. This special also featured an exciting stand-alone tale about the WWII hero Captain Midnight, by Joshua Williamson, Pere Perez and Roger Robinson, and a solid story from "Avatar: The Last Airbender" by Gene Luen Yang and Ryan Hill.

7 G.I. JOE: A REAL AMERICAN HERO (2010)

GI Joe Real American Hero 155

Throughout the 1980s and 1990s, Larry Hama was one of the leading minds behind the success of "G.I. Joe." Among other things, he wrote Marvel's "G.I. Joe" comics for over a decade until they ended with "G.I. Joe: A Real American Hero" #155 in 1994. For 2010's Free Comic Book Day, gave Hama the opportunity to continue writing "G.I. Joe" right where he left off over a decade earlier.

In "G.I. Joe: A Real American Hero" #155.5, Hama and Agustin Padilla put the focus on Cobra when one of their world-domination schemes actually began to work. With familiar characters like Cobra Commander, Destro, Storm Shadow and Baroness, this villain-centric tale had enough moments to satisfy die-hard fans and intrigue new readers with faded memories of the Saturday morning cartoon. In the comic's finale pages, Cobra activated sleeper agents around the United States in a seemingly successful takeover attempt. This intriguing cliffhanger fed directly into IDW's revived "G.I. Joe" series, which is still ongoing and being written by Hama today.

6 CAPTAIN AMERICA AND THOR: THE MIGHTY AVENGER (2011)

Captain America Thor FCBD

In the summer of 2011, two of Marvel's cinematic titans made their debuts in "Thor" and "Captain America: The First Avenger." Naturally, Marvel's 2011 Free Comic Book Day release brought both of these characters together in "Thor and Captain America: The Mighty Fighting Avengers." This all-ages special was produced by Roger Langridge, Chris Samnee and Matt Wilson, the same creative team behind the short-lived but critically-acclaimed all-ages title, "Thor: The Mighty Avenger."

In this issue, a modern day Thor and WWII-era Captain America were transported to Camelot, where Loki has taken Merlin's place during King Arthur's search for the Holy Grail. After a brief fight with a hydra, the real Merlin revealed himself and helped the future Avengers defeat Loki before sending them back to their homes. While Langridge's script moved along well and brought out the humor in both characters, Samnee and Wilson's art really shined here. With strong, clean lines and sharp colors, this utterly fantastic art combined classical cartooning with modern storytelling sensibilities and made for a crystal clear reading experience.

5 SCOTT PILGRIM (2006)

Scott Pilgrim

By 2006, Scott Pilgrim was on the rise. Although "Scott Pilgrim vs. the World" wouldn't hit theaters for another few years, the black-and-white indie comics sensation had already amassed a cult following with its mix of humor, romance and action over its first few volumes. In their 2006 Free Comic Book Day offering, Oni Press released "Free Scott Pilgrim," a 17 page "side-story" by Bryan Lee O'Malley starring some of the title's characters.

In the story, Scott fought some randomly-generated clones of a movie actress and tried to pick out a drink at a convenience store with his friends Ramona and Wallace. While most of the Scott Pilgrim series was focused on its over-arching narrative, this was a rare vignette that let readers simply hang out with the characters. Since the third volume of the series, "Scott Pilgrim & the Infinite Sadness" was released a few weeks after this title, it was the perfect time to introduce curious readers into the increasingly popular graphic novel series.

4 THE NEW 52: FUTURE'S END (2014)

Futures End FCBD

After the success of the weekly series "52" in 2006, DC launched several subsequent weekly series to varying degrees of success. In 2014, DC used Free Comic Book Day to launch the weekly event series "The New 52: Futures End." With work from a slew of A-list creators including Brian Azzarello, Dan Jurgens, Keith Giffen and Ethan Van Sciver, the special showed a dark, deeply weird version of the DC Universe's possible future.

In that future, most of that world's heroes and villains had been turned into monstrous cyborgs by the Brother Eye artificial intelligence. As the few remaining heroes, including Batman, began to fall, Terry McGinnis' Batman Beyond traveled back into the past to change the timeline and prevent this future from coming about. Although this title was criticized for its hyper-violent, almost macabre tone upon its initial release, this apocalyptic future effectively set up incredibly high stakes for the rest of the series. Along with the inclusion of beloved former-Saturday morning cartoon star Batman Beyond, this made for an eye-catching debut with a compelling central narrative.

3 AVENGERS (2009)

Avengers Thor Jim Cheung

After years of upheaval, the Marvel Universe was in a fairly odd place in 2009. While Norman Osborn led S.H.I.E.L.D. and a team of government-sanctioned Dark Avengers, Wolverine, Spider-Man and Luke Cage were part of a ragtag group of New Avengers. These two drastically different teams met in Marvel's 2009 Free Comic Book Day release, "Avengers" by Brian Michael Bendis, Jim Cheung and Mark Morales.

In the issue, the two Avengers teams battled each other before teaming up to defeat Ymir, a Frost Giant, with the help of Thor. By using Spider-Man as a narrator, Bendis was able to ground the proceedings with some of Peter Parker's famous wit. Despite a packed cast, the proceedings never felt crowded or rushed thanks to some of the slickest work of Cheung's career. With plenty of room for Bendis' trademark dialogue and Cheung's dynamic action scenes, this standalone team-up tale was an accessible entry into one of the odder periods in Marvel's history.

2 TRANSFORMERS VS G.I. JOE (2014)

GI Joe Transformers

Tom Scioli and John Barber's "Transformers vs. G.I. Joe" miniseries is one of the most astounding licensed comics ever published. While this 2014 series could've been a route team-up, the almost psychedelic series contained the full might of an overstuffed toy chest and a hyperactive imagination. On 2014's Free Comic Book Day, IDW unleashed the first issue of this series, "Transformers vs. G.I. Joe" #0, on an unsuspecting public.

In the story, the Transformers Starscream and Bumblebee fell to Earth in the middle of a fight between the G.I. Joes and Cobra. With numerous nods to obscure aspects of both franchises, most of the action followed the Joes as they battled Cobra's genetically-engineered "killer vegetables." Where other comics in these franchises have kept fairly close to their established source material, this title channeled influences like Jack Kirby and 1980s action movies into a bombastic adventure. While this issue didn't leave much room for the Transformers, it established the series' unique blend of whimsy, action and energetic artwork. The book's final pages included extensive text pieces with page-by-page commentary from the creative team.

1 AMAZING SPIDER-MAN: SWING SHIFT (2007)

Spider-Man Brand New Day

Just a few months before Marvel controversially erased Spider-Man and Mary Jane's marriage, they used Free Comic Book Day to give readers a preview of Spider-Man's new status quo. In "Amazing Spider-Man: Swing Shift," Dan Slott, Phil Jimenez, Andy Lanning and John Dell offered their back-to-basics take on the Web-Slinger.

In this pitch-perfect adventure, Spider-Man tried to apprehend the vehicle-controlling villain Overdrive while delivering a cake to Aunt May for her birthday. Filled with villains and members of Spider-Man's classic supporting cast, this was an ideal comic for new and lapsed readers alike. In addition to Overdrive, this issue introduced Mr. Negative, Jackpot and Officer Vin Gonzales. Over the course of the next few years, all of these characters went on to play fairly major roles throughout Spider-Man's "Brand New Day" storyline and beyond. With Slott's quippy dialogue and Jimenez's hyper-detailed art, this title served as an accessible entry point for new fans and offered a perfect start to one of Spider-Man's most refreshing eras.

Don't forget, Free Comic Book Day 2017 is Saturday, May 6! Stay tuned to CBR for all the latest Free Comic Book Day news, and let us know what your favorite Free Comic Book Day title is in the comments below!