i firmly second the meditation--sometimes that's the ONLY way i acn de-stress, and you don't need hours to do it, which is good. Sometimes only 5-10 minutes of quiet, eyes closed, breathing slowly while visualizing...heck, anything peaceful, generally (i like to imagine clouds moving with the breeze across the sky--it might sound cheesy, but it IS peaceful! ;) can really do wonders. :)
Write a story, whatever comes to mind, helps me work things out; or just play countless hours of Call of Duty Black Ops 2 earning those K/D's. (cough3.5ratiocough)
Any of those or a combination should do the trick :)
But, if you want a recommendation, playing video games sorta takes out some of my stress. That may work for you, who knows @w@