I would say that any comedian who has appeared in a commercial is not funny. I'm sure I will be contradicted shortly.
Also: for the most part (here's where I'll really get the flames), Will Ferrell is not funny. Except when he's doing his impersonation of James Lipton. Even then, it really only works when he's across from Lipton.
Neither is David Spade (except in Emperor's New Groove, and he was well supported there) or Adam Sandler.
Chris Farley was never, ever funny--just painful.
Just in case you think I merely hate SNL, I think most of the early comedians were fantastic, even if they've started to fade now. Dan Akroyd comes to mind, as does Tom--err--John Candy, and of course Steve Martin.
