8. HOW I MET YOUR MOTHER (CBS, 2005-PRESENT)

Mystery: Who is Ted Mosby's wife?

Narrated by a future version of Ted (Josh Radnor) as he explains to his kids, in 2030, how their parents met, the sitcom has managed to keep fans' attention for seven seasons without yet revealing the identity of Ted’s wife. Though it is a central mystery, the writers keep it on the back burner, doling out only a few key clues per season as the man's romantic history plays out, women seeming like sure bets before they take themselves out of the running. (Or do they?)

The result is a show that treats the eventual answer more like a sweet dessert at the end of a long, satisfying meal rather than the main course. The show’s humor and non-linear storytelling are the real key here. We’re not sure anyone could have predicted that one of the best TV mysteries of the decade would come from a sitcom, but that's the beauty of television.