I would have to go with Lewis Black and Mitch Hedberg with my most recent fave's. I love Dave Attell but I never saw any of his standup besides the intro's to "Insomniac." Our local stern replacement morning show has a guy that's pretty funny, Earl David Reed, but have never seen him perform. The squirelly guy that was the cop that stops Jim Carrey and Jeff Daniels in "Dumb and Dumber" is very funny, but I've only seen his standup once on TV.
I also like the old school stuff with Eddie Murphy, Robin Williams, Jon Stewart, and Dana Carvey.........