Saw Killswitch Engage/Hatebreed in a tiny little tavern that held 300 people, an absolutely incredible show.
Lamb of God/Shadows fall was pretty damn incredible as well, their double basses would smack the shit out of your chest, great energy.
Also saw Metallica with Godsmack in 2003. One incredible show. I've always loved Godsmack, they put on an incredible live show, fantastic energy, loved the crowd.
Metallica was incredible, played their old classics, played Blackened, and especially Creeping Death.
There is nothing like chanting DIE! with 11,000 other people, it's almost reminiscent of a Lord of the Rings movie or some epic battle, it was great.