Rise Against (melodic hardcore/pop punk)
The Agonist's singer is a vegan and super duper animal rights activist, though I don't think a lot of it comes across in her lyrics.
Machine Head has a couple of songs off The Blackening aimed at war, religion, etc. (specifically "Clenching the Fists of Dissent" and "A Farewell to Arms")
05/06 - Misery Index
07/19 - Rise Against/Killswitch Engage
08/08 - Slipknot/Lamb of God