Well I'm into energy and having fun at shows. Therefore the best ever to me was Pantera/WhiteZombie a while back.

honorable mentions:
Jagermeister two yrs ago w/ hatebreed, Arch enemy, and Slayer (=not a crowd, just one big mosh pit)
Black album tour:Fight, Suicidal Tendencies, and Metallica (the previous metallica that is)

More recently:
Soulfly-hope to see em' again this week!
Cannable Corpse w/ Hypocrisy
Superjoint Ritual (nuts...chicks stage diving topless into one gigantic pit)

Hope to see soon: Lamb of God, Maiden, Shadows Fall, Malmsteen, Slipknot, Chamira