Most of these are not going to be either under-the-radar or recent, but neither of those were stated criteria, so hopefully no one will mind. :)
Not sure where you draw the line on what constitutes "metal". I don't think most metalheads (at least, those that listen to modern metal) would count much of what I listen to as anything harder than "hard rock", but....
Anyway, I'll try to tread carefully in that respect. :p

- A.A. Bondy: "How Will You Meet Your End"
- Most stuff I've heard by ††† (a.k.a. Crosses) would fit. My favorite song of theirs with which I'm familiar is "Trophy" (though the version I like best is a non-album version that's not on YouTube).
- Chris Cornell: "Steel Rain" (Extremely depressing and a little spooky!)
- Bush: "In a Lonely Place" (Joy Division/New Order cover)
- Joni Mitchell: "Woodstock" (Also worthwhile is Chelsea Wolfe's cover, which is still haunting, if slightly less enthrallingly "weird" than Mitchell's original)
- Cruel Black Dove: "Wasting" (I much prefer The Vandelles Remix, if you can find it somewhere) & "Offer"
- Black Prairie: "Red Rocking Chair"
- Fever Ray: "If I Had a Heart" (I get the impression that anyone with a penchant for darker-hued electronic music is way ahead of me on this recommendation, but better safe than sorry)
- A fair bit of Eric Heberling's excellent score for The Elder Scrolls: Daggerfall qualifies. Here's a playlist that I found of "night music" (using remade tracks, though they seem fairly close to the originals); dunno how much of the dungeon music is in there, but most of that would be right on target for this thread

I'll post more some other time, if I remember.

Don't forget Arena's OST. While much of the music was re-used in Daggerfall, some of it was not. Notably, the tune that plays when you enter a house illegally (for example, by successfully picking the lock) and are sneaking around the house is not in Daggerfall.

(By the way, that part of the game is highly unrealistic; when you're in somebody else's house, monsters will spawn extremely frequently, and you will not find inhabitants trying to go about their normal lives. Also, there are no lasting consequences to doing this,)

This isn't an exactly obscure one, but anyway, one from Finland: Amorphis - The Bee

Username Hawester contextualizes the Finnish mythology behind the song better than I ever could, but even without that I somehow find the song rather captivating - the small inevitably taking over what is left of the great, and creating glory of their own. Reminds me of Dark Souls in a way, and inspires me to make notes for a tabletop RPG campaign. Maybe one day.

Bohren & Der Club of Gore - Black Earth (on the Tube)
Bohren & Der Club of Gore - Sunset Mission (on the Tube)

Ahab - The Call of the Wretched Sea (on the Tube)
Moss - Cthonic Rites (on Bandcamp: 01. Crypts of Somnambulance | 02. The Gate | 03. The Gate II)

SleepResearch_Facility - Nostromo (on the Tube)
SleepResearchFacility - Deep_Frieze (on the Tube)

I've been slowly crawling through everyone's posts, and I appreciate everyone who contributed. I'll post a few more songs to keep the thread going.

Steve Roach, Suso Saiz - Earthman
Snakes - Young American
Bat Nouveau - Death Mask
Allicorn - Outsider

As for metal, I want to clarify that
this
this
and maybe this

are acceptable, but stuff like

this
this
and this

are a bit too cheery, just to give examples in broadly similar categories.

Joking aside, rules are not definitive, post what you deem fits the thread.

Sadly, I don't expect this topic to live a long life. Anyway, thanks for mentioning something I've never heard of! (Yen Pox)

ps. I love all Peter Andersson's projects - same for the other Peter Andersson (Lina, Deutsch Nepal) ;-)

I'm going to stretch the definition of "dark" here (and the definition of "music", as well), and mention John Cage's work 4'33" as a possibility. It's the sort of work that, if it were a light show, would definitely be considered dark.

Thought of another great example. In Undertale, the music that plays if you kill every enemy in an area and then get into a random encounter is very dark and creepy. (I believe it's not in the soundtrack or any of the data files, as it's just a slowed down and pitch lowered version of another track.)

Then again, Undertale does have a track titled "Battle Against a True Hero".

I'm going to bump this thread with some more music before it's considered actually dead. Wouldn't want to let it go to waste, do we?

XDZVONX - Simple Witchcraft
Clan of Xymox - The Rain Will Wash Away
Rosegarden Funeral Party - Gaslighting
Dalek - Few Understand

Maybe I should've mentioned it in my last post, but unless otherwise noted, I take only the music (instruments and vocals) into account when evaluating songs for darkness, spookiness, etc., not the lyrics.

- Wye Oak: "Mother" (Danzig cover)
- Fleetwood Mac: "Rhiannon"
- Alan Jackson: "Midnight in Montgomery" (I don't listen to much country in general anymore, let alone popular, mainstream country; but what I do like tends to be darker or sadder or -- as in this case -- spookier)
- Ministry: "Paisley"
- Timber Timbre: "Lay Down in the Tall Grass" (This song is kind of borderline; I'd describe it as "kitschy-spooky" -- perhaps others might call it "spoopy")
- Dax Riggs: "Night Is the Notion"
- Chris Cornell: "Mission" (This one's sort of weird and woozy-sounding, rather than being morose like "Steel Rain" from the same [excellent] album, but I'd say it still qualifies as a bit dark and unsettling, musically)
- J. Tillman: "When I Light Your Darkened Door" (This one's kind of borderline as well, riding the line between merely sad-sounding and actually chilling, but it's good enough [despite the rather lo-fi recording] that I can't not mention it)
- White Zombie: "Blood, Milk and Sky"
- Alice in Chains: "Rotten Apple"
- Joseph: "Sweet Dreams"

Julee Cruise - Into the Night

Angelo Badalamenti - Mulholland Drive

Whiskey Lullaby (Wikipedia)

Tiamat have always had a dark-entrancing sound to me (mainly due to their heavy industrial influence at times), but I guess that may be subjective. Not sure if it's the kind of metal that gets past the bar, but... hear for yourself :):

Tiamat - Gaia
Tiamat - Do You Dream Of Me

Oh, almost forgot to share probably the most haunting guitar solo of all times. silly me :P:
My Dying Bride - Edenbeast

Cryo Chamber on YouTube

Dark Lantern by Mandragora Scream

Cut Forget by Omega Lithium

Swingin' Hatches by Rye Town's Creatures

Vampire by Xandria

Nightmare by Nyxx I also suggest two others from her: Diabolical and Voodoo

I have plenty others to post but this is a start. .. if this thread keeps going....