Overkill is somewhat underground. Despite that they should of been in Metallica's spot on the big four. The Sign of the Southern Cross is an awesome band that only has 800 fans (I'm one of them). They sound somewhat like Pantera, their lead singer is awesome. Also, Throwdown is pretty awesome. Another very awesome band that plays metal somewhat like Pantera.
Ummm a good death metal band would be vital remains. look up dechristanize by them. not much into death metal more into black metal so look up cradle of filth, dimmu borgir, carach angren, and chthonic