Well, my post is pretty useless I guess.
I really don't know of too many bands that really focus on acoustic, but I'll just give some random thoughts on what I know? I'd be really interested in it, so I'd like to see some other responses anyway...
Pink Floyd - Meddle is a great mostly acoustic album.
If you have not, definitely check out Nick Drake. He's a much older artist, put under the "folk" label, but it's really awesome. He uses a lot of different tunings that give him a very unique guitar sound (and he plays it quite well, I might add). Also, he's a brilliant poetic lyricist (although it slighlty shows the time difference). He died young, and left only 3 LPs.
If I'm not mistaken, Mikael mentioned Nick Drake before in some interview or something? Either way, I'd certainly try to hear some of his music.
I don't hear many artists that focus on acoustics the way Opeth does. Many will incorporate it, but Opeth really brings it to the forefront. I know I'd like to see more bands that did...
Also, Camel is wonderful. I haven't heard much by them, but you can definitely hear Opeth being influenced by them. I plan to buy an album by them soon.
Anyway, I hope this was of any help to you.