Ive seen:

Slayer
Lamb of God
Children of Bodom
Mastadon
Thine Eyes Bleed

this was all at the unholy alliance tour last summer, although I never heard of thine eyes bleed untill then I thought they were cool because after their set the guitarist came out and went into the moshpit with us for the rest of the show. Killer show I definitely recomend seeing all of the above bands for all you metal heads.

This summer I plan on seeing slayer again in august and I'm also gonna be going to the free ozzfest if I can make it down to connecticut.