NFL/Rappers/Olympus is out. I think those ideas are so terrible that if every person in the entire world liked the idea, I would literally have omni switch control of the thread to someone else to make the change. That's how much I hate those kind of ideas.
Come on guys, this should be real simple. Something cool and exciting, and probably cartoony.
Actual pokemon and not gym leaders isn't a bad idea. Kingdom Hearts characters, FF7 and/or Dissidia characters, DBZ, Different colored power rangers or characters (like Ivan Ooze). Metroid Hunters? Punchout characters? Fire Emblem classes ( i personally love this one). Members of the tantalus. Castlevania heroes. Sonic Riders characters (lolz). Enemies from earthbound. Final Fantasy VI characters. There are like 6000 options here.