I always try to remind myself that since I have bipolar disorder eventually what goes down must come up (that being one of the diagnostic criteria and all). I just cling to that.

I also listen to music that makes me happy or watch movies that make me happy.. if that doesn't work sometimes I go for a movie that I know will make me cry - sometimes it's cathartic but that's only something I do if I'm pretty sure I'm only depressed and NOT suicidal or in danger of becoming a danger to myself.