Here are two Super-Hero roleplays:

[url=http://www.roleplayerguild.com/topics/76031-all-star-marvel-audax-mundus-novus/ooc]All-Star Marvel[/url]
[url=http://www.roleplayerguild.com/topics/135-create-a-hero-rpg/ooc]Create-A-Hero RPG[/url]

The former (All-Star Marvel) was just recently started, so you don't need to ready any encylopaedias to get caught up.  Plus many of the Avengers (Iron Man, Hulk, Thor, etc.) are currently open for applications.

The later, while it has been going on for over a year (and technically more than that if you count pre-GuildFall), uses original characters.  Furthermore, even though there are several posts, one of us can easily catch you up on events and such.

Also, if you are more into DC comics, you can look at [url=http://www.roleplayerguild.com/topics/76754-dc-universe-age-of-heroes/ooc]this roleplay[/url].  They have not even started yet, so there is zero information that you need to get caught up on.

Hope that helps!