Moon Knight is a good one. He's got a cool costume too.
What about some of the lesser Avengers? Giant Man, Hawkeye, Vision, Wasp or Black Widow if your into that sort of thing. Everyone knows Cap, Iron Man, and Thor but seem to forget about the other members.
Dr. Strange? Somewhat obscure, at least in the public eye. Plus you'll get to grow a sweet beard.
For Villains, you can't get much more obscure/wacky than Clock King!
Also, he's not a "real" superhero but Minuteman from Freedom Force would be an awesome costume. So would The Crimson Chin.