"Midnight Lullaby" By Odd Project is great, soothing mood music. Kinda depressing though. All their other stuff is metalcore, brilliant stuff. I recommend.
BoySetsFire is kickass, agressive and sad.
Undeclinable are sad too.
Face Tomorrow are just DEPRESSING.
'Never Stops' by Lagwagon always gets me down, but thats for personal reasons.
The Juliana Theory is great depressing music. Some of their songs make me cry just by listening, though some also sound really poppy, but sad.

Well, hope they "cheer you up".

Chaos