While Colbert and Stewart are damn good, I'm talking real talk show.
My vote goes to Conan O'Brien most definitely. Even on days where I would rather gouge my eyes out than force a smile, Conan can still get a chuckle out of me.
Space Ghost was decent too, but, let's face it, Space Ghost was 5 minutes of funny and 10 minutes of 'meh' (most of the time).
Edit: http://www.youtube.com/watch?v=Jr6wdEkONN8
The best of both worlds, Conan on Space Ghost. "You died baby. You gotta get down with that."
ReEdit: Ace, yeah I was thinking that, but I can't change it now, it's too late, the dice are rolling.