Whenever I'm feeling down, I listen to music and do nothing for a while. This works surprisingly good, however; if you're like me and have your player in random mode, then you've experienced the cruel twists of fate that lead you to listen to incredibly sad songs when you were feeling down: to avoid all that, you should have a good playlist of uplifting songs. Here are some that you probably know of:
New Radicals - You get what you give
Sometimes you might just not be in the mood for incredibly upbeat songs; this one keeps a good balance between optimism and relaxing melody. As a great plus, the lyrics might really cheer you up.
Counting Crows - Mr Jones
This melody has a sense of nostalgia within, that isn't necessarily a bad thing, however. Avoid looking too deep into the lyrics while listening to it. They are a bit ambigous and open to interpretation, unlike the former which is pretty straightforward.