Anthing I can do to get down a mountain on snow including alpine skiing, telemarking, snowboarding, etc.. Motorcycles (used to be cars, but Chicago winters eat cars), photographic equipment, Mountain biking and now computers..
One of the biggest and most expensive hobbies has been audio though. I had a high end dedicated 2 way system that was worth about $20K at one point and now have it pared down to about $6K of the "essential" stuff. I'm even thinking about going smaller because I don't have time to listen as much as I once did now that I'm more into computers. I also like mp3's. Not because of the sound quality, but because I can sample so much music. I love being able to hit shuffle and not hear the same song twice in a single day of listening. I've never be able to do that with anything else.