I'm glad the different versions of Superman got a mention. I think it can be a good trail to follow, if a character is popular enough to sell comics, its probably going to get ripped off.
Spiderman probably has his fair share of rip offs.
Various Super Teams seem to have a trend in mimicing each other.
Best Rip Off goes to the series Hyperion is in, what was that called again. They had like rip offs of what seemed like just about anyone and everyone. I need to try to find a reputable place to buy that online sometime.
Actually, I'm a little surprised there hasn't been a mention of Captain America rip offs or Wolverine rip offs yet. Maybe just because they are blatantly obvious or remain within the same comic universe or something?