I found music helps alot, not that depressed emo stuff, but more upbeat songs with rhythm like David Bowie and the Beatles.
I use newgrounds flash portal aswell, the humorous stuff to be more specific. Really just anything funny I can find on the internet helps.
Seriously though, everything around you effects your mood. Sights, sounds, smells, etc. So if you are listening to sad music when you're sad, it can help because sadness goes in a curve, there is a point you must lower yourself to in order to get through a problem but most people push that too low, then climbing back up is hard.
I was put on every variety of uppers and downers from lithium to zyprexa, some paxil, prozac, ritalin, everything. I spent from 11-16 on these weird pills. They couldn't find a pill combo to make me happy and it turned out that I was the key player. The drugs made me spacey, the spaciness effected my logic and I was unaware that that angry system of a down I was listening to(SoaD was still screaming the majority of the time) Slipknot, Mudvayne, Metallica(oh so sad they're in this list, they're so good but it's true: Master of Puppets was a pretty sad album), etc. I was spending months at a time watching Fight Club on repeat, all kinds of drug movies where people hit rock bottom. It became an obsession to hit rock bottom.
I did. Now I'm on my way up..I'm not suggesting you try for rock bottom at all, I'm actually suggesting you change your environment. Put in some brighter light bulbs, buy a lighter colored piece of clothing. Switch your soap to something citrusy so you can be known for smelling fruity. A lot of stigmas we give ourselves become the character traits of who we are.
It's really hard to give you good honest help in such a short time, maybe if we talked more I could offer some suggestions and we can work on something.
Good luck :)