How about a little more Kirby love? Obvious reason I went with an Avengers cover, although the FF featured more monsters (right on their first issue is one of the most famous comic book beasties ever). Still, Lava Men clearly fill the bill.
Notice the early guest star appearance by the Hulk. The perpetually irate Hulk had left the team after issue 2 (not utterly without cause; although he quickly joined with Namor the Submariner to attack his erstwhile comrades), being more or less replaced by Captain America, who the Avengers found frozen and revived in Avengers #4.
The oddest thing is that the book not too long afterward abandoned the Marvel all-stars idea. Aside from the Hulk, Thor, Iron Man, Giant-Man and the Wasp all left the team and as of issue 16, there was a major roster change (such shake-ups becaming sort of an Avengers tradition) with Cap leading a much less powerful line-up of Quicksilver, the Scarlet Witch and Hawkeye.
I have to admit, the Avengers line-ups never truly seem ‘real’ to me unless Iron Man, Thor and Cap are on the team.