As odd as it may sound, but it works for me, is Dance Dance Relvolution. I've been playing that game for over 7 years now, and it's always been a good stress reliever. I usually do play on heavy mode, but sometimes just playing standard or difficult mode is good enough to bring a great burst of energy to me. It keeps me from thinking of alot of negative things. Plus the music makes me hyper. xD
Sometimes when I'm angry I'll go to the mall and go to a fav. clothing store of mine and just try on clothes. Even if they look ridiculous on me, at least I'm doing something than moping around. Going for walks and listening to your music player while doing that is good. Physical things usually take stuff off my mind.
Another good way is writing or drawing it out. When a boy I really, really loved turned me down... I went into a complete baw fest. Never had I cried so hard over a guy. My mom could tell I really loved him, and called his sorry a$$ and scared him enough to where he doesn't even look at me! Coward. xD
But I wrote a song about him. Ha! I should send it to him, but to be honest, I don't like getting stuff started. That just makes it worse.