Not just a pure comedian, but also a decent actor. His deliverance is great, and he's more natural than, say, Eddie Griffin or Kat Williams.
Liked him in every movie or show I've seen him in, starting with the first one - a movie titled "The Chateau", with Paul Rudd.
Is also very good in: Weeds, 40 Year Old Virgin, The Ex (small, but hilarious role), and Blades of Glory...
I need to go watch some of his other films.
Don't forget he played Hammer in that VH1 movie about from a few years back. But, I did like him in 40 Year-Old Virgin, he was pretty funny there.
As far as funniest black actors, I put would put Ced in the mix, except I don't think he's good enough to be a lead; he's much better in a co-starring role, where he's better playing off someone else. With Chris Tucker...dude's only done five movies in the last TEN years (Money Talks, a small role in Jackie Brown, and the Rush Hour movies). That's probably due to him overrating himself and asking for outrageous money to do these movies (he got something like $25 million alone for Rush Hour 3) like he's in the class of Will Smith and Denzel Washington. However, he's a funny guy.
I saw Katt Williams' HBO stand-up special, and I wasn't entirely impressed. I can take him in small doses, like in Friday After Next and Norbit.
Another underrated funny guy in movies beside Terry Crews (the dad from Everybody Hates Chris), is Kevin Hart. The scene in 40 Year Old with him going at it with Romany Falco was one of the funniest parts of the movie.