How about try running? It's a major mood lifter!
Granted, the first two weeks of running are a living hell, but once your body adapts you will suddenly find yourself enjoying your frequent runs and challenging yourself to run farther and faster.
I find it substantially lifts my mood and energy level all day long compared to days when I don't run.
I've had a great deal of sucess with this running program: Couch to 5k Running Plan