[code_beers]

Singing - it may not seem like there's much overlap, but the amount of pattern recognition and other compatible skills required is surprising. Flow state is a common element in both, and I find it a great stress reliever. It also helps to balance a left-brain career with right-brain hobbies.

Meditation - not really a hobby per se, but the amount of clarity it can bring to programming later that day is incredible.

Nutrition / health optimization - understanding how the body works and how to support it through your lifestyle and nutrition can be a hobby in and of itself, and as a bonus, it helps maintain a healthy brain to program with.

Cooking - this will save you money, gain you friends, and can be looked at as 'food engineering'. It's just chemistry you can eat, in the end.

Homebrewing - much like cooking, this is biology and chemistry you can eat. Or in this case, drink.

Geocaching - I've been meaning to try this. I gather it's essentially world-wide interactive scavenger hunts that use GPS.