Angel Dust
Aphex Twin
Baroness
Death From Above 1979
Drive Like Jehu
Electric Wizard
Freen In Green
Gama Bomb
Helios
Kylesa
Meshuggah
Mouth Of The Architect
Propagandhi
Puscifer
Russian Circles
SikTh
Skeletonwitch
Sleep
Sleepy Sun
Supercontinent
Warning
Weedeater
A lot of these band are far from "unheard of", but definitely not mainstream.