Cars. Reading about them, lusting after them, daydreaming about how to mod them. It's to the point of obsession. But not exotic cars, sports cars, muscle cars, or anything normal people like. I only like big 4-door sedans because I'm a weirdo.
Computer hardware. I love swapping out motherboards and upgrading stuff on computers. Probably more than even using them.
Electronics. Fixing things, replacing bad caps, designing and building circuits, soldering, I like doing that kind of stuff. I like modding and designing circuits for automotive projects most of all. Also like studying and buying test equipment.
Watching TV: serial TV shows, Nova, and some reality TV shows (Survivor, Amazing Race, Big Brother).

I would really LOVE to get into 3D Modeling, but so far to make stuff from scratch has been kind of hard and never got past remapping UVs and modifying existing meshes.