Oh lordy lordy lordy let's let 'er rip.
Buried at Sea. [http://www.youtube.com/watch?v=wf0zDNzPmHc] Funeral doom. Nothing too outstanding, but pretty good stuff.
Bull of Heaven. [http://www.bullofheaven.com] Noise "music" group, though half of their stuff isn't really music in any typical sense. Moreso just a mish-mash of sounds, tones, and so on. Some of their stuff is actual music in a more traditional sense, but you have to look for it. BUT THE BEST PART, ALL THEIR STUFF IS FREE.
Boris. [http://www.youtube.com/watch?v=ld0jEcFUFko] Maybe the best-known band on this list, because they're pretty big in the oddly "is a thing" overlap between sludge, doom, drone, and metal fans. Their stuff is epic beyond words.
The Gersch. Can't find any YouTube videos of their stuff so no link, sorry. They only put out one record and never got much popularity, but they were doing some early sludge in the mid-90s. As well as a handful of other genres in some big pretty neat fusion thingy.
Greg(o)rian [http://gregoriandoom.bandcamp.com/] (Bandcamp link, can't find them on YouTube). Doom band with some pretty awesome stuff, and it be free.
Sabazius. [http://www.youtube.com/watch?v=TVb8J_42H5I] Atmospheric ambient drone-doom or whatever the hell it is. It is what it is, and it is quite amazing. If you like Sunn O))) or the like, you'll probably get a big kick out of these guys. Like a lot of bands here, their stuff is free.
Sorne. [http://www.youtube.com/watch?v=uNwO-L9d0TA] Not a metal group. They just started up earlier this year, if I recall. I saw them live in Houston a few weeks ago and their show blew my mind. It was absolutely incredible. I'd recommend them to basically everyone with somewhat eclectic tastes.
Algol. [http://nulll-void.com/nulll/releases/037.htm] Space-ambient and, surprise, free. Almost totally unknown as far as I know.
Any of Stijn van Cauter's projects. [http://www.metal-archives.com/artists/Stijn_van_Cauter/29445] Most of their stuff is free and available through the label that I linked to for Algol up there. A lot of it is pretty extreme funeral doom, but with a heavy drone and ambient touch and a semi-noise touch.
Faal. [http://www.youtube.com/watch?v=PKfMSDC9JD4] I actually don't know what their popularity status is, so I'm gonna risk it and post a link to them anyways. They're a doomy band.
Ea. [http://www.youtube.com/watch?v=IScOIXxszDo] Basically, they're Skepticism, but Russian. Doom metal but with a strangely beautiful sound to it in most cases.
Mars Red Sky. [http://www.youtube.com/watch?v=6L1pmdvmSWc] French metal band, pretty awesome song that I linked to (or so I think).
Chuter. [http://www.last.fm/music/Chuter] Shoegaze/experimental project from some British dude.
Jared Konkle. [http://www.youtube.com/user/Jedwink] Basically just a dude in his house with a guitar and a mic. He does a lot of covers on his YouTube channel, but he does some original songs too which are great. He does a kinda country/folky sound. Pretty great stuff. Oh, and he has an album for free via Facebook of original material.
That's all I got for now.
