I highly suggest using
http://www.last.fm/ to find bands similar to the ones you already are into.
http://www.pandora.com/ may also be of help to youl; however, it does not have much of the music i enjoy.
Some bands to consider:
Lamb of God (mostly As The Palaces Burn)
Decapitated
Severed Savior
Cryptopsy
The Black Dahlia Murder
Gojira
Origin
Into The Moat
Uphill Battle