There are a bunch of supers games out there, and several for Marvel specifically.
For an old, simple standard, you might go look at the first of the Marvel games, which can be found at
Classic Marvel Forever*, buried in the menus. Many folks these days would hate the design, but it is simple, allows a lot of creative play, and is pretty god for pickup play.
The new Marvel Heroic Roleplaying Game, from Margaret Weis Productions, is also an awesome game, based on the CORTEX rules. It is less simple, and I find the presentation of some of the concepts a bit clumsy, but it is still a great game.
*I must note, I am actually skirting our rules here. I can't speak to the legality of that site. Nowhere does it say they're reproducing the content with agreement of the copyright holders. On the other side, it has existed for years. If it isn't legal, the holders are willfully turning a blind eye.