Like Noodle, I'm a PC builder in my other spare time. I also do online gaming (Team fortress 2 at the moment, but really any first person shooter). I was very heavily into the clan scene a few years back, but now much prefer playing around with mates in a much less formal manner.
Occasionally play squash, not ridden my bike since my wrist-destroyer of an accident back in January.
I suppose work is sometimes my hobby, too. When you get to play around with 3D models of proteins, it can be quite fun!
Probably the biggest time-consumer, which I suppose much be a hobby by default, is DIY. My wife does most of the gardening, and I do most of the "home-improvement". Currently doing the finishing touches to the bathroom, then it's onto the lounge and dining room...
And of course spending time with my lovely wife :)
Roo