Slipknot...they were part of a large bill, Linkin Park, Papa Roach, and Mudvane (who didn't play).
Papa Roach wasn't terrible but the lead singer sang half the songs with his wanker out. Not sure I understood the gesture.
Slipknot, whose music I don't mind, was just an aurel assualt. I lasted 1 1/2 songs before my buddies and I couldn't stand it anymore.