I used to be a trekkie. It all went downhill after Next Generation, though...
I'm was a piano major in college, so I could go on for a while about cool classical music and theory (if I can remember it all....).
I love reading about art history - particularly European. The different eras fascinate me (Renaissance, Baroque, Rococco, Classical, Romantic, neo-classical, impressionistic, etc).
I love going wine tasting.
I'm sort of an audiophile. I'm obsessed with good sound. Just got an SACD player a few weeks ago (sounds incredible). Love going into Hi-Fi shops to listen to expensive speakers. I also really like headphones (not the cheapos you find at Walmart or Best buy, but really good headphones that can sound better than speakers that cost $1K+). I actually have a pair of headphones that originally retailed at over $200.
I have a weakness for computer games, particularly military ones (see computer games thread). Ghost Recon drains way too much time out of a day if I let it.
I like watching the discovery channel/history channel/animal planet/national geographic, etc...
I used to be a big airplane nut. I could tell you all about jets and helicopters and any kind of aircraft.
And the biggest one of all:
I hang out on an internet forum frequently.