Will Ferrel is a genius. One of the greatest.
I generally really don't like Will Ferrel, but there are a handful exceptions. Blades of Glory was perfect, as was his tiny role in the Wedding Crashers.
On the other hand I really like Robin Williams. There are definitely films I don't care about, but he's willing to take on a reasonable spread of different kinds of roles and many of them very well. Dead Poets Society, Hook, Good Will Hunting, Good Morning Vietnam, Ms Doubtfire, Aladdin (where he wrote most of the lines for the Genie which the animators then worked with, rather than the other way around) there is plenty of good stuff and it has a good range. I also love some of his older standup, like the one where he describes different types of drugs.
As for Jim Carey, same thing for me - not all his films are great, but he is stil absolutely genius and there is plenty of really good stuff. And even when he is overacting, he brings something unique to the table that very few can do. I love when he rewinds himself in Ace Ventura (among others) or the fight he has with his own hand in Liar Liar.
But Yes Man is really very good, with some good acting also by the rest of the cast, can really recommend it.
Oh, and while we're at it, I saw Inglorious Basterds a while ago, and then saw a bit of it again this weekend, and I only kept watching because it was near the end and I wanted my wife to see that, so I could spare her the full movie. I thought it was a bit more pulpy than it needed to be. Really didn't like it at all. I saw another Jewish resistance movie recently that I thought was much better, even though that was pretty mediocre too.
Looked it up, it's Defiance and I'll rate it 6.5/10, vs Inglorious Bastards 5/10. IMDB rates them 7.2 vs 8.4, so I guess I don't agree with popular opinion there.