If I had time to burn, I would take some kind of auto-mechanics class or electronics class in order to have the skills to mod my car for less $$$$. (Dammit Jim, I'm a keyboard jockey, not a gearhead!!!!!!!!!!)
You could also learn Tai-Chi (moving meditation). It's great for your long term health. I have been practicing it for 10 years. If I had the time (i.e. discipline) to practice every day, I would be in really great shape right now.
I've found that multiple hobbies can be entertaining -- when one gets old, you can go to the next one (or if one is out-of-season due to weather, etc). You can always go back to the old one again, or if it sucked, now you know
It may sound corny, but if you can incorporate a hobby into volunteer work for the community, that can feel pretty good too. If you like driving, deliver for meals-on-wheels, for example.
Think about what made you happy as a kid and go from there...
lol like mine is building stuff. always have always will. (sometimes stuff just doesnt need to get built by my hands...) never really been into sports or anyhting but outdoor stuff i love to do. hence my current job is mowing grass and doing general yard work. i also fix lawnmowers (again goes back to the building fixing things)