Spiderman - shy geek turned superhero. What's not to like? Probably the comic book hero I identify most with. :-P
Abyss - this supervillian essentially has a black hole in his chest with which he sucks up his enemies. That's pretty much the pinnacle of badassery in my book.
Wolverine - what a great character! Superficially he's quite a brute, but underneath his tough image, he's a very deep, conflicted guy.
Herbie Popnecker (not very well known, but pretty cool) - a little boy with limitless power & a taste for lollipops. I loved it when he became the Fat Fury. Wikipedia article on Herbie
The Saint of Killers - a very dark anti-hero. Or maybe a villian? An invincible gunslinger with 2 revolvers that never miss & always kill their target.
That's all i can think of off the top of my head. Good thread!