Alot of death metal bands such as Soilent Green, Suffocation, The Haunted, Misery Index
If I had to name a rap artist it would be Immortal Technique, although he is getting bigger, he's an excellent poet, not some asshole obsessed with money cash and hoes like 99% of the popular rappers these days.
I also believe the stoner rock band Kyuss is underrated. Although they had a cult following in California in the 90's they pretty much created stoner rock and deserve more credit for that.