I just heard Neun Welten's new one last night. good stuff
The genre's called "neofolk" for future reference (not like Agallochs new stuff, which is some kind of folk metal, but their old stuff and Nest etc.).
October Falls (not to be confused with american pop band October Fall) is very similar, especially in the fact all their songs are instrumental like Neun Welten (But their NEWEST album, 4 songs long, is actually new Agalloch style!!! I was so shocked aye, after how similar their first two albums were, all acoustic instrumental neofolk)
Empyrium is another one in the same vain, very moody, and they have a mix of neofolk and gloomy folk metal albums in their discography
Ulver's album
Kveldssanger you probably know about, that's their own neofolk album, very nice sound.
Ainulindale's
The lay of Leithian has a similar sound to that album of Ulver.
Foresti is a favourite of mine. female vocals and woodwinds frequent their songs, rather than being strictly acoustic guitar like the aforementioned.
You may also know viking/folk metal band Månegarm recently came to the table with a neofolk album of their own,
Urminnes Hävd - The Forest Sessions
Arcana's album
Le Serpent Rouge is perhaps their best, and very 'atmospheric neofolk' a lot more like Nest than the others (Burzums'
Hlidskjalf is in similar vain), though they have a medeval slant to their stuff. and Raison d'être is at the extreme end of atmospheric neofolk, it's pretty much just 'noise' ya know? but may wanna check out their album
In Sadness, Silence and Solitude just to see what it's all about.
Harmaa has this awesome dark sound, and is very piano based, very unique.
Belborn is pretty unique, using synth a lot, and having a huge range of material, from beautiful dark stuff like "Chor der Toten", to upbeat songs like "Verblutet" (the most dancey song called "Bled to Death" you'll ever hear) and just beautiful neofolk like "Eure Tranen Bedeuten Nichts" ('Your Tears Mean Nothing')
Halgadom is another BM style band to try their hand (and they have some amazing ones in both genres), I can't recall how much of
Verdunkelung des Göttlichen is neofolk, maybe all of it, but most of their other albums are straight up BM. but I have a clip of one of my favorites of theirs online
here.
Orplid is another unique one. great deep vocals. rather diverse material they have but I LOVE the songs like "Erster Frost", "Bifrost" and "Auf deine Lider senk ich Schlummer".
Tenhi is very cool, putting a lot more effort into drumming and creating a real
band sort of feel you could actually nod your head to (check out "Lualuin Sinulle")
Argine are another with a a varied discography, a sorta spanish rock sound, check out "Lucente Anima"
There are some rather generic bands like Darkwood and Of the Wand and the Moon, a lot of their stuff sounds the same and rather repetitive, but they have their good songs. also some I never really got into or who have very scarce discographies, but you may like, Graumahd, Weihan, Nebelung, Dies Natalis, and Carved In Stone.
Espers is an American neofolk group with a strong hippy culture vibe, female vocals, you really get that woodstock vibe from their guitars aye, which may not be what you're after, but their albums are worth checking out if the decription doesn't sound horrible. at least check out the song "Dead Queen" or "Cruel Storm" which could easily have been a popular song everywhere like Sigur Rós' "Svefn-g-englar" was.
Edit: there's a few one-off very nice instrumental neofolk songs off metal albums which you may also be interested in...
Catamenia - Outro
Finntroll - Rök
Garmenhord - Intreedinghe
Hordak - El Lago Enol
In Blackest Velvet - In Blackest Velvet
Kalmah - Svieri Doroga
In Flames - Acoustic Medley
In Flames - Pallar Anders Visa
In Flames - Timeless
Old Man's Child - In Quest of Enigmatic Dreams
Pagan Reign - With the Power of Fallen Heroes
Pagan Reign - Skorb'