A few months ago I came across an amazing thrash band called Aspid from Russia. They released one album in 1992 and broke up shortly after only to be lost in the abyss of dead metal bands.

Aspid- Extravasation

Any others you can think of?

Hell yeah brother, D.B.C.'s self-titled 1987 album & the Fearless Iranians 1988 album Holy War! even Leeway's Desperate Measure's album has been left in the void for like 20 years

Your request is rather vague - what exactly are you looking for? Bands who only released one album or demo and then split up and which someone happens to consider amazing? Bands which released more than one album but split up a while back? How obscure- von and timeghoul obscure, or even more so? Do obscure bands by now fairly prominent artists count? (crux, thou shalt suffer) what about bands little known to the wider metal community but with a strong regional fanbase?

there are 1000's of bands like the one you mentioned in OP!

There's quite a bit of discussion in the Heavy/Speed/Power thread (if you're nuts like me and want to read all 135 pages!). Maybe this belongs in each thread specifically, e.g., Death, Black, etc.

'Cause there are way too many to count. And not all were good. Not all were Cyperus.

To clear up any vagueness in my post, I guess I'm looking for metal bands people find to be amazing, pre- y2k, that released any sort of material, then broke up or are still around and still almost no one has heard of them.

I'll be sure to check out those other threads as well.

It might be wise to dig into those threads, but, as far as power metal goes, my favorite "unknowns" are Cyperus (check out only the two demos, not the full-length), Blind Illusion, Armoros, Abandoned, Glacier.

I'd have to say the death metal band Brutality, having only released three albums and than disbanding. I've always really enjoyed the band, but haven't met many who have heard them, which is kind of sad I think.

I'll say Galaxy (or Galaktika, whatever) from Russia. Very obscure, and very forgotten, but their second album is pretty cool speed metal with glam vocals/lyrics and keyboards.

Psychotic Waltz springs to band. They are a progressive metal band with a huge psychedelical undertone who released a streak of four excellent albums during the early nineties. While the discription of a psychedelic "hippie" metal band may sound rather corny, their music is rather good.
I have not yet fully delved into their discography but I can say they surely are skilled musicians with some excellent songwriting going on. Awesome music!

Fixed.

I would like to bring the doom metal band Electric Void Summoner into context.

Sindrome was great. Only released two demos, but they were both awesome. Also, the thrash/death band Solstice never seems to get much recognition

these bands are obviously not forgotten, because you guys still remember them.

Good point, guess we better lock the thread because it's impossible to discuss a forgotten band.

However, using our versatile understanding of koleekial english speaking, we can determine that by "forgotten" the op meant "relatively unknown".

Many bands come to mind, but one band that really should have made it big was Warlord. They had some really awesome songs with a lot of melody, killer riffs and solos, and some very inspired lyrics. They couldn't keep a singer, so they eventually broke up after the release of an EP and a "Live video Soundtrack." The drummer went on to play for Fate's Warning's Ray Alder era albums after they disbanded. They redid a bunch of old songs and a few new ones with Joachim Cans from Hammerfall on an album they put out in the early 2000's, but they haven't done much since then.

Kralizec, Patrick Loisel's band before Augury, is too often forgotten due to the success of Augury, when in fact Origin is pretty much a precursor to Concealed, and in some ways even better.

Black Knight and Cirith Ungul.

Cirith Ungul!!?? Ackk! Ok, fine!

Although this is a somewhat newer band, Exulcerate is a great death metal band that has somehow managed to go under the radar. Their album Remnants of a Cannibalistic Debauchery was one of the best death metal cd's i've heard in a long time.

Carrie
War Machine
Acid
Trop Feross
Original Sin
are a couple I can remember at the moment but many in my music library are mostly Female fronted bands.

I do have another pile of forgotten metal bands I managed to salvage off a site i downloaded but I have yet to listen to any of them. I'm still on the first volume, on the first band, Exodu (which is also a good forgotten band by the way.)
There's also the band Fatal Violence and Warhead which are good male fronted bands (I believe they weren't included in the pile but good bands)

Theres a thread here somewhere on underrated/forgotten gems, you should find it, it was pretty interesting.

Crematory (Sweden) and Morpheus Descends. Ass kicking old school death metal thats hardly ever mentioned.

I'm just going to mention a few because there are so many:
Demented Ted
Jumpin' Jesus
Brutality
Eructation
Resurrection
Soulreaper
Voor
Massacra

Ved Buens Ende fits here? It has already been recognized but it is not popular and well known like the other 90% of Trv3 Norwegian BM of the nineties...

Malevolent Creation
Oppressor
Solstice
Disincarnate
Vader
Morpheus Descends

None of these bands receive the credit they deserve.

I'll mention Antagonist (USA), a thrash band that released their first EP in 1994 which would have been better suited for the late 80's. The violence and thrashability of Bonded By Blood coupled with the relatively open song-writing and groove of early Megadeth and a hint of the tech-thrash scene = massively underrated thrash greatness. I think that it's actually my favorite EP.

I've mentioned the band before on here, but with Tuagh disbanding the project people really should check out Askival. The album "Eternity" is one of the best albums I've ever heard and almost certainly my favourite pagan black metal release.