Here's #39! Click here for the master list!
Tales of Suspense #39
Talk about a hard-luck loser! Amazing Spider-Man #39 contains the first work that Jazzy John Romita did on the title as well as the revelation that Norman Osborn was the Green Goblin!
Such an issue is an absolute classic in comic book history.
Sadly for that issue, it is also an absolute runner-up to the first appearance of Marvels' latest movie star, the Invincible Iron Man, who made his first appearance in Tales of Suspense #39.
Iron Man is notable for being one of the creations that Larry Lieber, Stan Lee's brother, worked on, although mostly as a scripter, if I recall correctly. Also, remarkably, Don Heck was the artist on the first Iron Man story, although almost certainly someone else (likely Kirby) designed both the initial armor AND the later armors (Kirby did the cover - and it is an awfully neat cover).
The origin of Iron Man is a great idea, so good that the recent film barely changed it - not many other origins in comics can claim THAT!
What other notable #39s are there...FF #39 was a good issue, as was Sandman #39. Swamp Thing and Doom Patrol both had good #39s, Justice League America #39 was in the midst of the famous "you want serious? Here's serious!" arc by Giffen/DeMatteis..any other book I'm missing?