Eddie Izzard is at the top of my list, because a lot of his act is improv. He can't go by a script because he's dyslexic. Plus, the whole transvestite thing just tops it off.
Also, Jim Gaffigan: One of the few comedians who can get good laughs out of people without using profanity.
Dane Cook has a great stage presence, but he's almost the exact opposite of Gaffigan when it comes to profanity.
i just found Eddie Izzard recently. i like his act a lot, but when he girls himself up too much, it's distracting. the Dress to Kill DVD is just awesome though.
Other of my fav's are: Lewis Black, Ron White, Denis Leary, Bill Engvall.