First off, I hope this isn't too vague a topic to enquire about.

I don't normally pay as much attention to the number of members and musicians which a band has as I should, but I'm more interested of recently, for two reasons - firstly, and foremost, I'm curious to sound what kind of sound such bands have, and where it differs from black-metal which makes use of more instruments. Secondly, I want some inspiration for my own work, which I hope to involve only a single-guitar in, if possible.

I'm open to black-metal of more or less any variety, and as obvious as you like - I'll probably end up saying "Oh, they're a three piece?" quite a lot.

I'm only looking for bands who uncomprimisingly play as power-trios, including in the studio.

Darkspace

http://www.metal-archives.com/bands/Darkspace/13746

Averse Sefira, who unfortunately just broke up.

Absu?
http://www.youtube.com/watch?v=5ZDowNse1Fk

Dammerfarben's first and only album to date was a 3-man job, even though they picked up a few more people recently...
http://www.youtube.com/watch?v=1QUs6L6RTF8

And here's one where you'll definitely go "Oh, they're a three piece?"
http://www.youtube.com/watch?v=eGjgthbNNWE

EDIT: Took one out because they use more musicians live...

"cascadian" band Fell Voices is a 3 piece. Their drummer does vocals live without a mic, it's pretty wild.

Here you go.

Carach Angren

If you mention Darkspace you might as well mention Paysage d'Hiver, side project of the guitarist/vocalist and is equally if not more awesome.

Immortal, duh.
http://www.metal-archives.com/bands/Xibalba/4232 Check out Ah Dzam Poop Ek.
Fell Voices are amazing, that video, Inspector_Satan, is fucking ridiculous. As in brilliant. That fucks up your voice though, I've done it before in a really small venue and I can tell you, the set better not be longer than 30mins.
Hmm after further investigation, it seems like he is screaming into the mic in the bass drum, which will give it an awesome effect. Soft, distorted, deep and dense over the speakers of the venue, with some added echo, and then the higher pitched notes will pierce your ears directly. Damn fine live execution.

EDIT: I was unaware of the nameless reference to Immortal earlier in the thread by he who shall not be named.

Old Ancient Rites : The Diabolical Serenades - Blasfemia Eternal era.