I've thought about this too. How about Andy Griffith? Or Bill Murray?
Yes, I was thinking about adding them and I'll probably be adding more.
Thought of some more unfunny people who are good actors: Bonnie Hunt (Green Mile), Tracey Ullman (Panic), and Jim Belushi (Salvador).
Bonnie and Tracey as unfunny people?
Not on my planet...
L. Bangs (no, I won't tell you what color the sky is here! ;) )
Just remember Janeane Garofalo in the Minus Man
I heartily agree with all of them except Robin Williams. He can (very) occasionally turn in a good role if he has a director to reign him in. Otherwise, he's glurgy and over-the-top. I will never forgive him for Patch Adams. Or What Dreams May Come. Or Bicentennial Man (which admittedly I didn't watch all of).