Other than those already mentioned (especially Napalm Death, Metallica and Lamb Of God)-
Brujeria- Other than the devil worship and drug taking/selling themes, there are some interesting ideas in there
God Forbid- They called an album Consitution Of Treason, I think they were trying to make a point there...
Gojira- Did an entire album about the saving the whales. Good as it might be, that still therefore makes them hippies
One Minute Silence- Are they metal, are they not? Before you post a reply, remeber I don't give a shit either way.
Pitchshifter
Sepultura
S.O.D- Fuck The Middle East, amongst other clasics
And I can't believe that Slayer haven't got a mention yet
But of course, real metal is all about well buff, half naked, half leather clad men covered in baby oil. Obviously.