Looking at the industrial compilation and tribal industrial threads, I was thinking about how landmark and solid the Twilight Earth - International Soirée CD is. A classic compilation and one of the more significant ones in my history. A great foundation for anyone tempted to learn.
Are there any others? Ophir? Ahimsa? Those aren't as focused as Twilight Earth, but I think of them in the same area. There was a second Twilight Earth, but I don't think it compares.
As for artists, one of the greats is Tuu, though they later ventured into a more new-agey arena when they joined the Fathom label. It's worth looking into Franklin and Parkin's other work outside of Tuu as well. Some of Jorge Reyes' tracks are phenomenal and quintessential if you're interested in this subset of ambient. He's a bit inconsistent and varied, which can lessen the impact of his albums, but The Flayed God, Mort Aux Vaches, and his prehistoric series are highly recommended.
I wish I knew more of Steve Roach, or had the stomach to work through all the muck, because he has some really good albums when he drops into darker territories. I believe he's been playing shows, or maybe just small events, again. Some nice, epic live recordings have shown up at the Dime Tracker in the past few months. I have to appreciate how prolific this guy is. He's a workhorse. I know he breaks down his own work into several categories: tribal-ambient, desert-ambient, atmospheric space, healing arts, etc. I can't attest to how reliable his own delineation are though.
Which then leads into probably the best known of this style: Vidna Obmana. If you were around experimental music at all in the 80s and 90s, you at least heard a track or two of his. Lots of comps. Lots of notoriety. I know very little of him, so if someone else could talk about him, that would be welcomed and great. I know I'm more interested now than ever.
There are other groups not known for this style that I feel tread awfully close. An example is Endvra. They have some beautifully flowing ambient that is accompanied by fluid tribal drumming. The more recent Vasilisk - Tribal Zone could also be considered akin to all this.
I'm sure I'm forgetting other obvious names, but in haste, I wanted to get this thread started.