Just a few recommendations of mine:
The Mars Volta -
The Bedlam In Goliath
Another mindblowing album, requires more than one or two listens though, even if it's not quite as hard to digest as their last two records.
Between The Buried And Me -
Colors
Best metal album ever in my world, absolutely epic in every way.
The Dear Hunter -
Act II: The Meaning Of, & All Things Regarding Ms. Leading
Ultra talented band from Boston, they mix elements of rock, pop, post-hardcore and folk and avoid all the clichés. Great guys to chat with too.
Wintersleep -
Welcome To The Night Sky
My favorite Canadian band. No quite as dark and moody as their previous one, but still as genuine as it gets.
The Dillinger Escape Plan -
Ire Works
The undisputed kings of math-metal, ridiculously skilled musicians, and now even strangely catchy.
Pelican -
City Of Echoes
Not quite as heavy and epic and it used to, they took a slightly lighter direction, but it's still heavy-as-fuck instrumental music.
Also, I couldn't find a good picture of Day Without Dawn -
Understanding The Consequences, my favorite of 2008 so far. Super underrated, almost completely unknown band from NJ, for fans of The Postman Syndrome (their former name), Tool, dredg and Isis.