Katt Williams and Dave Chappelle are definitely my two favorites and a little bit of Dane Cook occasionally. I'm really sad there isn't much of Dave Chappelle anymore, though
My personal favorite is Ricky Gervais. He is a comedic genius, and he's even a great screenwriter. He's an acquired taste, however, so I'm sure a number of people will disagree with me here.
I knew I had posted this in a different thread somewhere, so I decided to dig up what I said about Ricky Gervais rather than try and remember what I said before.