I usually kick back, put on my headphones, launch foobar2000, and listen to some music. While doing this I will typically play a game chosen from my game folder. One of my favorites is Heboris (Unofficial Expansion), a Tetris clone for Windows. (if you want, I'll share with you how to get it). If it's not that, then I might choose some sorta danmaku game. Then again, those aren't always the most stress-relieving.
Or, failing that, just spend some time resting. By resting, I mean in a bed, eventually falling to sleep.