SOLITUDE PRODUCTIONS runs a 24/7 radio, mostly for anything Doom Metal related.
666MrDoom - everything Doom/Stoner Metal
b4keve00 for everything that is Black Metal underground. The channel has slowed down a lot but is still worth checking out.
Captain Beefart for everything that is Psychedelic (Rock).
For more Black and Death Metal (and edgy stuff):
Cosmic Hammer
DEATH FETISH for all the weird psychedelic Black Metal stuff that Black Magick SS has started.
Dot Dot Dot - Death and Black Metal and a lot of obscure bands
More Psychedelic Rock stuff:
Eternal
Grindwar Channel: Grindcore, Death Metal, Crust/Punk
Harakiri Diat: everything Punk, Psychedelic and obscure
HeavyStonerDoomBlues - the name says it
John Smith - no new uploads anymore but lots of old Heavy Metal albums and gems from the 70s/80s
MrStonerBeliever and
MrStonerBeliever2 - both dead but lots of Doom/Stoner stuff
Mao da Gloria - Underground Black Metal
NewWareOfOldSchoolThrashMetal - Thrash Metal
No Gleaming Light - Black Metal, Death Metal, Crust/Punk
NoPunksInK-Town - Death Metal, Grind, Crust/Punk
NoFunNoMoshNoCoreNoTrends - Death/Black/Thrash Metal
NotesFromTheUnderground - all sorts of Underground Metal
NWOTHM - Heavy Metal
ObeyTheRiff - Doom/Stoner/Psychedelic (dead but still a good channel for digging)
OdiumNostrum - Death/Black Metal (if you like DEATHSPELL OMEGA you will find a lot of DSO inspired bands there)
Rare & Obscure Metal Archives - well, lots of rare and obscure old metal stuff. One of the best channels out there.
ROB HAMMER - Doom/Stoner/Psychedelic
Stoner & Doom - dead
TheBongDruidOfMammothWeedMountain - dead (Stoner & Doom)
ThePsyFrost - obscure underground Black Metal stuff
Underrated Albums - Not really Metal related but lots of obscure bands. So fucking awesome.
Veterans Of The Psych Wars - More obscure and psychedelic stuff. And the guy behind it wears a tin hat and sometimes starts to rants about politics in the comments and his channel community section. Hilarious.