Stand up comedians - agree with David, the Big Yin takes some topping. I also loved the old style British ones, like Les Dawson, and particularly Dave Allen. Nowadays I like Michael Macintyre as well.
George Carlin, Louis Black, and Dave Attel.
Louis CK is probably my favorite.
John Pinette, hands down.
The Dice Man (Andrew Dice Clay) is NOT funny.
The only comedian that ever made me laugh by putting a lot of obscenity in his act was the original, the one, the only George Carlin.
Mod Edit: His 7 Dirty Words routine set the bar that comedians still aspire to. Track it down on YouTube, but beware that it is NSFW or appropriate for young ears.