I was pretty seriously depressed for a period of about 6-8 months a few years ago for a whole lotta reasons. It took me a long time to get out of it and the catalyst to getting out of it ended up being just going out and having a good backpacking adventure in the mountains with some friends. It was the worst fucking trip ever and we nearly died but it changed my attitude, I came back and started exercising and taking care of myself. I found an awesome thing I could be passionate about and things just seemed brighter.
So my answer is appreciating my friends, exercise and snowboarding I guess.
For my days or weeks where I seem to feel like crap in more recent times I'd say the above plus music. There's always something to help you deal with frustration, sadness or pretty much anything.