I swim a mile. I've been doing it for about 15 years so it's automatic and almost meditative, plus a full-body workout. Surprising how much head work I can do in that half hour.

I also paint, but you can probably insert any totally immersive creative pursuit here (music is probably more common amongst hackers). It completely switches brain hemispheres and unlike programming, my mind does not wander at all when painting, and I can literally go to another place for hours. Unlike when swimming, I can't think about programming or anything at the same time, I am completely absorbed in the painting. Paul Graham has lots to say on the subject.