The original animated version of Teen Titans is often cited as one of the most influential DC adaptations of its day. Several aspects (and characters) unique to the series made their way to official comic book pages, and the show itself remains an acclaimed and celebrated piece of children's animated programming.
Robin (Dick Grayson), Starfire, Cyborg, Raven, & Beast Boy composed the main group of Titans, with their ranks expanding throughout the series. They made so many allies throughout the show they were able to make other Titans teams, such as Titans East (and Titans North & South in the tie-in comics). Out of all the added Titans, these heroes, in particular, stand out the most.
10 Thunder & Lightning
Thunder and Lightning were the first Honorary Titans to appear onscreen, debuting in the fourth episode of season one: "Forces of Nature." The two are brothers with unknown origins but seem to be supernatural spirits of Earth. They are initially unfamiliar with societal standards and use their powers to destroy various parts of Jump City. For their entertainment, of course.
Lightning is more trigger happy than Thunder, with the latter being more open to listening to others and recognizing the wrongs they've caused. Both were manipulated by Slade to combine their powers, creating a monster of fire. Upon the two of them realizing the harm they'd done, they combined their powers once more, this time bringing about a rainstorm that extinguished the monster. They also helped The Titans fight the Brotherhood of Evil, but both were captured.
9 Aqualad
Aqualad is the second Honorary Titan introduced in the series, saving The Titans from a watery grave in the episode "Deep Six." Helping The Titans takedown the villain Trident, Aqualad later appeared as a particiapant in The Master of Games' battle royale. Afterward, he assisted in tracking and taking down Brother Blood. In the process, he also helped form and joined the Titans East with Bumblebee, Speedy, and Más y Menos.
He was among the victims of The Brotherhood of Evil, getting captured and flash-frozen after The Titans were ambushed. When he was freed, he helped clean up most of The Brotherhood's army, literally washing them away.
8 Pantha
Pantha is introduced late in the series' final arc, where Cyborg attempts to warn and inform her about The Brotherhood of Evil. She's a pro-wrestler, possessing super-strength, durability, and endurance. Her combat prowess was so great; she was able to overwhelm several of the strongest fighters in the series, including Cyborg, Atlas, Adonis, and Cinderblock.
After The Brotherhood was defeated, she went on to help form Titans South.
7 Hot Spot
Like Aqualad, Hot Spot was a participant in The Master of Games' tournament. Upon the tournament's conclusion, Robin made everyone present (aside from Aqualad [as he was already an Honorary Titan] and Gizmo) Honorary Titans. Hotspot later became one of the first targets of The Brotherhood of Evil, who wanted to use his communicator to track The Titans across the globe.
After a long-fought battle against Madame Rouge, where she deceived both Hotspot and Robin by shapeshifting into them, Hot Spot was captured and flash-frozen. After he was freed, he fought within The Brotherhood of Evil's base, enacting his revenge on Rouge with Wildebeest and Jinx.
6 Jericho
As one of the last people to receive a Titans Communicator in the series, Jericho's screentime is limited but memorable all the same. He tends to avoid conflict if possible, secluding himself to a high mountain meadow (much to an exhausted Beast Boy's chagrin). Still, he was more than capable of fending for himself, being one of the few Titans to defeat his attackers when The Brotherhood of Evil executed a global strike.
Jericho can possess others, which grants him access to all their powers, knowledge, and memories. This power was vital to securing an entrance to The Brotherhood of Evil's hideout and allowed Jericho to cause its members to essentially fight themselves. In the tie-in comics, Jericho also helps to stabilize Raven's powers, helping to put her Emoticlones - the different aspects of her personality - back together. His connection to Slade is unfortunately not explored.
5 Red Star
Though he only had a significant role in one episode, Red Star certainly impacted both The Titans and audiences. A former soldier, Red Star gained near invulnerability, super strength, and the ability to project radioactive blasts from a government experiment. The experiment also left his powers unstable, which caused him to go into a self-imposed exile.
The Titans meet him in Siberia after he rescued Starfire from a blizzard, who'd been tracking a radioactive monster (that Red Star had inadvertently created). Following some encouragement from the Tamaranean Princess, Red Star decided to fight once more, even at the cost of his powers turning irreversibly unstable. Though he disappeared after a radioactive explosion, it was implied the explosion allowed him to exert full control over his abilities. He later reappeared to fight The Brotherhood of Evil and joined Titans North.
4 Herald
As with Jericho, Herald is one of the final Titans to receive a communicator. He resides in an alternate dimension, accompanied only by his horn, which grants him interdimensional travel. Though villains Warp and See-More attack him during The Brotherhood of Evil's world-wide (and cross-dimensional) ambush, he manages to defeat them both.
He later joins up with Beast Boy, Pantha, Jericho, and Más to assault The Brotherhood of Evil's base in Paris, further participating in the fight when other Titans reinforcements arrive. His assistance saves the day, transporting a primed fusion device into space to keep The Titans alive.
3 Kid Flash
Introduced during the final stretch of the series' run, Kid Flash claims to be "one of the best" superheroes around. After the Titans East had been called back away from Jump City, Kid Flash filled in for them. He caused particular problems for a group of villains called H.I.V.E. Five (technically six), led by the supervillain Jinx. The speedster took an immediate liking to her, opting to talk with her instead of immediately arresting her.
He helped her realize her true potential for good and picked her up on his way to fight The Brotherhood of Evil. His brother-like relationship with Robin is explored and deepened in several tie-in comics. He also officially starts to date Jinx, despite his constant flirting with others.
2 Jinx
Originally appearing in the series as a villain, Jinx turned over a new leaf in the final season of the show - with some help from Kid Flash. She'd believed herself incapable of being good because of her powers, which manipulated probability. After attempting to get the attention of The Brotherhood of Evil - Madame Rouge in particular - Jinx became disillusioned with villainy.
She then left her team and seemed to go into hiding with Kid Flash. They both assisted the rest of The Titans in the final fight against The Brotherhood, where Jinx took out her entire (former) team, Mother-Mae Eye, and Rouge herself. Jinx additionally made various appearances in the tie-in comics, where she continued to prove her worth as Titans material.
1 Bumblebee
Bumblebee was first seen alongside Jinx in H.I.V.E Academy, a school for supervillains. It was later revealed that she'd been working with Aqualad to obtain information on the H.I.V.E.'s leader, Brother Blood. She later joined The Titans in taking down Blood's aquatic base. Afterward, she became a member of Titans East and was usually the only person to take their duty seriously.
When Cyborg rejoins the original group of Titans, Bumblebee effectively became Titans East's leader. Her powers, demeanor, and leadership skills cement her as one of The Titans' most reliable allies. She escaped capture at the hands of The Brotherhood of Evil and later traveled with Red Star and Starfire to the final big battle of the series.