Antiques Roadshow! (US and UK)
But seriously, I'll watch Jeopardy when I get the chance.
My all time favorite, however, is Only Connect. Even though a lot of the questions are (understandably) UK centric, I'll manage to get 2 or 3 questions correct and maybe even 1 or 2 on the connecting wall. Victoria Coren is brilliant, love her intelligence and wit.
Oh, Eggheads isn't bad, either.