Lots of great stand-up comedians already mentioned...Carlin, Hicks, Chappelle, Oswalt. BTW, I think all of Carlin's classic HBO specials are still on Netflix...some of those specials from the 90s are amazing and essential viewing if you consider yourself a fan of comedy.
I just skimmed this thread and I'm not sure I saw anyone mention Louis C.K. yet. He had already made a name for himself as one of the best stand-ups around, but then he went out and created the great tv show Louie. He pretty much does it all...writes all the episodes himself, directs, edits, etc... It all comes from one guy, not the watered-down lowest common denominator product of a group of writers.
Also don't think I've seen anyone mention Doug Stanhope. He's primarily known as one of the two guys who took over hosting The Man Show when the original two left, but that show fucking sucked so don't let that put you off. The guy just wanted a nice paycheck. His stand-up material is very dark and filthy, so obviously would appeal to readers of this board, hehe.
Two of my favorite TV shows while in highschool were Strangers With Candy and Upright Citizen's Brigade. That might have been the best hour of TV comedy ever.
