D&D easily. My dad played it when he was in high school, and I guess I inherited his love for it. Me and my friends started in grade 7 and still play almost weekly, even after our DM Chris, who was bloody awesome, left us. And it's not just D&D, we play all sorts of tabletop games, like Anime D20 (I'm a Magical Girl, it's awesome), Shadowrun for like a month, and now I'm trying to get some Rifts books and start some games with it.
Other than that, Magic is huge at my school. I built myself a new Red-Black-Green Wither deck a month ago, but I still lose to my friends's cheap ass Blue-Black with Academy Researchers and Fool's Demise. We make our own cards too. If me and my friends can get a good game of Mafia going it's awesome, could last anywhere from 5 minutes to 3 hours depending on how ruthless our storyteller and killers are. Not huge on board games, but we always play Pictionary with my creepy cousin whenever we see him, and it gets really messed up. I'm another creep that likes Scrabble, but meh.