Video games (particularly ones that aren't too much of a pain), watching movies - especially watching my favorite past nostalgia films make me feel all happy and comfy XP, listening to music, going for a walk and morphine, lots of morphine.
People say listening to your favorite music is best for relaxation, which it is usually, but other times I just need a change up, lest my favorites become my themes for stressful work. XD If you have a free moment, try looking up some new music to get into (or just revisit something you haven't listened to in a LONG time). When I find a fresh new song I love it actually makes me feel more peppy while working.
I also really don't believe you have to listen to stuff that fits the mood of what you're working on. Sure, when I work on Daniel I'll sometimes want to really get a feel for it and listen to '30s music or some really creepy stuff, but other days? Screw it, I'm listening to The Go-Go's.
Ehm, sorry, went into a different sort of rant about music there...