Fantastic Four #25-26 are cool for multiple reasons. First of all, it is the first meeting between the Avengers and the FF (taking place between Avengers #4 and #5). Also, it is the first time when the concept of the Hulk getting stronger the longer he fights is introduced.
So some background. Basically, the Hulk's little pal Rick Jones is now hanging out with Captain America; you know, cause Cap's an awesome living legend. The Hulk gets distinctively piqued, and so sets off to smash the Avengers. He starts pointlessly tearing up the town, despite knowing where the Avengers' meeting place is (having been a member). Eventually the FF, who as usual are having some emotional difficulties…
…decide to help out a bit and tackle the Hulk, who easily defeats them. As Hulk leaves the Thing in a chagrined heap, he has this awesome face that keeps making me crack up:
This is the kind of thoughtful intensity I want to see from the Hulk in future movies, people!
Anyway, the FF aren't down for long, and soon the Avengers are on the scene as well. This leads to an awesome fight; check it out in this great Kirby panel:
Here's another cool thing about the Avengers: the Wasp actually helps out for once. As you can see in the above picture, the Wasp is usually nothing more than a stinging example of the Smurfette Principle. Also she seems to faint a lot:
But now she actually plays a key role in defeating the Hulk, in a quite nasty way, no less:
All in all, the story seems pretty cool, you can check out more about it here (read the comments–trolls can be hilarious!). The price of these books together is about $2,600, which is well out of my budget, but oh well.