Not to turn this into a blog-type thread, but I was reaching pretty disgusting levels of awful mental conditions yesterday, to the point that doing something fatally stupid was becoming quite tempting, so I threw on Converge's "You Fail Me" and basically renewed my defiance and resolve to stick around. So while it didn't make me "happy" per se, that definitely elevated my mood in a positive manner.
I've found that I like to listen to really atmospheric rock, along the lines of Dredg of the Deftones when I am in a pleasant mood, and that stuff makes me happier.
Good hardcore records - American Nightmare's "Background Music," Modern Life Is War's "Witness", Defeater's "Travels," stuff like that - makes me happy. It's angry sounding music, but if makes me happy.