George Carlin. Because he didn't tell jokes, he just pointed out how f**ked up and broken life is... and we laughed.
Robin Williams. Because he had me doing literal roflcopters, and because he's the only guy I know who's done more drugs then me.
Notable Mentions:
Louis Ck, Chris Rock, Jim Carrey, Jon Stewert (The Daily Show), Anthony Jeselnik, and regulars for annual Roasts on Comedy Central.