Whenever I'm feeling a bit stressed or low, I fire up Celestia and spend some time virtually roaming the heavens. It's fun, edjumacational and relaxing. Especially if you listen to a Space Night compilation while doing this.
(Space Night is a German TV show that plays ambient techno and trance and shows images from space. Frito-who has lived in Germany-says it comes on after the clubs close, so I guess you're supposed to "chill" to it. Cool idea, no?)