So here's my list of people that I can watch for an hour and not crack a smile, followed by people that crack me up with almost everything they say. Note some of the people listed are the characters that they've played.
This is probably part one as these are people off the top of my head.
Ben Stiller (unless he's doing impressions)
Shemp Howard (3 Stooges)
Steve Martin (used to be funny)
The Schmenge Brothers (John Candy and Eugene Levy from SCTV)
Larry Fine (3 Stooges)