Corey brought up a bunch of good bands. As far as some more metalcore bands to check out, I suggest...
God Forbid is a really good American metalcore/thrash band. You can really see the Gothernberg influence in their first few albums, but they're starting to find their own sound. If that is not enough of a reason, they are amazing live and their vocalist Byron is one of the coolest/most approachable guys in metal.
Caliban brings the goodness from Germany. Musically they're really tight and Anders from In Flames has produced some of their stuff. Plus, their two splits with Heaven Shall Burn were really good. I recommend HSB as well.
Dillinger Escape Plan is really good with their metalcore/math metal/fusion sound. I know Corey will cringe, but if you like DEP check out Candiria. Their sound is undescribable and all over the place. In the same vein of that is Yakuza, which is metalcore with a heavy jazz influence.
Also check out some of the early crossover bands like Vision of Disorder, Madball and Ringworm.