Fear Factory - Demanufacture
I saw korn, FF and static x all on one bill and static x were by far the best band. I love FF but they aren't quite as energetic or as intense as they were the first time I saw them. Korn are a polished band but wayne static has the freakiest amusing voice live (exactly how it is on the albums, very few metal bands can boast that).
I saw slayer live with machinehead and slayer absolutely shat on machinehead. It was hilarious. I've been to a lot of metal gigs but slayer were by far the most "metal".
Straying away from metal, I would put the prodigy up there for decent workout bands. Lots of energy.