Never been much for boardgames, but the one I've always loved is Atmosfear. We had the old DVD version when I was a kid and it was just great.

It never takes too long due to the timer. No playtrough is the same due to the randomisation. And the way you need to work together against the evil guy on the DVD or everyone looses, while having work against each other to win over other players is just so well done. It's also complex enough to stay interesting, but not too complex to make it hard to play for non-die hard boardgame players.