These days I both work a day job and am a startup founder, and I don't do a whole lot other than work, between the two. But when I find (or make) a small bit of spare time, I like to do things like:
1. Read - fiction (horror, sci-fi, thriller/suspense, mystery, etc.) and various topics in non-fiction: physics, cosmology, history, economics, biographies, etc.
2. Mountain bike. I haven't been riding much lately, but this is one of my favorite outdoor activities when the weather is nice.
3. BMX - I still pull out my old BMX bike from time to time and do a little dorking around, street riding.
4. Road biking. I mainly only ride my road bike for cross-training purposes, but I like to get in a few miles here and there.
5. Hike and/or trail run. - I sometimes go hike or run, mostly on some of the same trails I MTB on. Plus a few nearby trails that are open to foot traffic, but not bikes.
6. Concerts - I love live music, and I try to make it to a concert every now and then. The last one I hit up was Trans-Siberian Orchestra back in November. But I like pretty much anything heavy-metal or hard-rock. From Steel Panther to Motley Crue to Tyr or Anthrax, whatever.
7. Dining out - I'm not exactly a hardcore "foodie" but I enjoy trying novel cuisine and having a good meal at a nice restaurant. So exploring new places to eat is something I like to do, especially when traveling. This week has been a good example - I've been in San Francisco all week (I live in Chapel Hill, NC) so I've had a chance to sample a Peruvian restaurant, a Czech restaurant, a place that specializes in garlic, etc.
8. I try to hang out at the local hackerspace[1] a little. Often when I'm there I'm actually working on the startup, but sometimes I like to go in and just tinker and play around a bit. I bought a few microcontroller / SBC boards (Arduino, rPi, BeagleBone) and a bunch of discrete components and shit, and built a monster breadboard with an integrated powersupply using an old PC ATX power supply. Sometimes I just go in and work on learning to build weird electronic circuits and stuff.
Outside of that, I dunno... does reading HN count as a hobby? Or watching TV shows and movies? I squeeze in a couple of "go to the theater" for a new release deals a year, and watch a movie on Netflix or Amazon Prime from time to time, or rewatch one of my old favorites on DVD. shrug
[1]: http://www.splatspace.org/