I like most Opeth (I thought Damnation and Deliverance both sucked, Ghost Reveries is pretty good but not as good as Blackwater Park or My Arms Your Hearse), and earlier In Flames records (Colony is my favorite).
I also really, really like stoner/art-metal bands like Isis, Yob, and Pelican (although Pelican are really just heavy post-rock a la Mogwai these days).
Also, Mastodon are probably the best "traditional" American metal band around right now. If you dig Opeth odds are you'll like Mastodon too, particularly their newest record Leviathan. They have a similar affinity for really brutal, speedy metal passages interspersed with crazy-weird chord voicings, although Mastodon take it in more of a blues-influenced direction than Opeth's more straight prog approach. Dudes are KILLER guitarists.
High On Fire rock pretty hard, and if we're going to segue into doom/stoner rock that new Earth record HEX is amazing (but not really metal, imagine if Godspeed You! Black Emperor did the soundtrack for a western movie).