Was I the only one who thought Andy Kauffman was the greatest comedian of all time?! Everyone kinda took a step back when he started his controversial wrestling career, but I was in tears. What he did for comedy was amazing.
Norm McDonald is great, too.
Besides that:
Steve Martin, Robin Williams, John Kerrys Vietnam Records, Jay Leno (not recently, but about 10 years ago), Eddie and Charlie Murphy, Paul Mooney, Lenny Bruce, Rodney Dangerfield, Johnny Carson, Seth MacFarlane (creater of Family Guy), and George Burns (God)