A few more...
I always thought Converge had really interesting vocals. Their production is absolutely filthy, for the techier sound that they go for.
Cattle Decapitation puts on a really good live show. Humanure will always be a classic in my eyes.
Oh, and nobody mentioned The Berzerker yet...
Their drummer is absolutely fucking sick!!! He gravity blasts like no other; I swear.
http://www.youtube.com/watch?v=_gqVVQ-q8Zs (No One Wins video)
http://www.youtube.com/watch?v=3JDj074-WP0 (Reality rehearsal in the studio)