Slayer always, except for the new one, the covers one, and the live ones.
12 minute sprint up the hill set that still works after 1.5 years:
show me your heart - need new body
stigmata - ministry
nwo - ministry
death's head - slayer
On the trainer:
loud hooky college rock (Pixies, Thermals, Cat Claw by the Kills)
grindcore (and specifically *not* death metal, which is too soloey/atmospheric for me - Nasum, Pig Destroyer, Rotten Sound, Cephalic Carnage, Kill The Client)