okay,
check out the new ISIS "in the absence of truth" which is a new direction for isis, with a lot of clean vocals.
'sleep terror' are an instrumental jazzy technical metal band
if you like the Arminian sound of system of a down, but not the lack of musical variety, check out 'Giant Squid'
If you havent heard tool, check them out. (you probably have)
there's not really a great deal of aggressive music out there without aggressive vocals
so with that in mind, here are some aggressive bands that show the diversity of the genre:
Superjoint Ritual (phil from pantera on vocals), Will Haven (hardcore metal), Cult of Luna (if you like isis), Pitchshifter (a blend of Drum and Bass and Nu-Metal, but better than it sounds), Opeth (Melodic Death Metal), Vision of Disorder (a blend of classic metal and hardcore), Meshuggah (very very very technical metal, difficult to get into, but worth it), Death (classic Death metal), Dysrhythmia (not really metal, very jazzy, coolness) Killswitch Engage (classic metalcore), Machine Head (British heavy metal) Orange Goblin (doomy metal with a party vibe), Pagan's Mind (progressive metal, bordering on power metal), Textures (hardcorish metal, check out 'polars' for a mix of clean and screaming vocals).
Obviously use your discression, some metal is not very accessible to people new to the genre, but there are a wealth of awesome bands out there, and to me nothing empowers the way that metal does. i hope you find a few gems in there, and find yourself lost in the world of heavy metal!!!