X-Men. I like the trilogy just fine, but a reboot in the vein of Batman Begins, where we get to see the origins of the team and the beginning of the whole humans vs. mutants conflict, could be great. I'd also like to see less emphasis on Wolverine. Hugh Jackman did a kickass job with the role, but the rest of the team played second fiddle to him and that really shouldn't be the case.
Why do some of you guys want to see Fantastic Four or Elektra get rebooted? As bad as those films are, I can't imagine a do-over would be any different.