I'd be torn between Lewis Black and Mitch Hedberg. And since their styles differ so greatly, I'll go with both.

Other notables that I find incredibly funny:
George Carlin
Stephen Lynch
Robin Williams
Jim Gaffigan
Dane Cook (I didn't think he was that funn at first - but he really grew on me. Funny guy.)

__________________
"My life is a furious ball of nothing."
~Dilbert