Video games... and SCIENCE!
This might be a bit of a rehash for some of you. But if you haven't heard about how awesome video games are yet, you should check this fairly current overview of studies on video games and their impact on the brain.
http://discovermagazine.com/2007/brain/video-games/article_view?b_start:int=0&-C
I especially like the in depth description of Tetris on the first page.