Soulfly are actually some ex members of Sepultura, which started getting some real popularity in the us in the early nineties. Speed metal is hege in south america and brazil, where Sepultura is from.
Lots of good metal out there, here are some of my present faves I'm listening to right now, if it's new to you check some of it out.
Between the Buried, the Dead , and me.
The newest Lamb of god album, As the Palaces Burn.
Mastadon...........burly stuff.
The Assistant
Atreyu
Burnt by the Sun
Darkest Hour
Converge.........classic hardcore
The Swarm, Parasitic Skies
The Hope Conspiracy (good stuff too)
Not Waving But Drowning
On Broken Wings
Poison the Well
Propaghandi, From Empires to Ashes... not metal, but if you have not heard this album, it rips.
Alot of this stuff is more hardcore than Metal, but whatever.
And BTW, Slayer kicked a$$. Always a great show.