Seems really cliche to say this considering the "Garden State" idea of pop-culture that surrounds them, but Iron and Wine actually have some very well recorded albums (Sam Beam is pretty much entirely acoustic with a few exceptions here and there) and EPs. I'd recommend "The Sea & The Rhythm" and "Woman King". They're both EP's but they're phenomenal in content.
ninja edit: It's worth noting that these are actually kind of low quality. His most recent album The Shephard's Dog is very well put together and professionally recorded. Also, the download only Bonnaroo album is very good as well (available on the bonnaroo website in FLAC for $13 and it's 2 "discs" if I remember correctly).
Acoustic Shards by Buckethead- Wonderful acoustic improvisations in the unmistakable Buckethead style
New Moon by Elliott Smith- Beautiful yet subdued playing with eccentric lyrics, one of my favs
Nirvana Unplugged- Self-explanatory- however, the guitar is amped, but whatever.
It would probably be helpful to know what kind of music you like. Acoustic music can run a pretty wide gammut.
At the risk of suggesting music that might not appeal to you, here are some albums that are very well recorded and have great music if you are open to it:
[size=small]Norman Blake - Whiskey Before Breakfast[/size]
Blake is an acoustic guitar virtuoso and his down home bluegrass style is
very easy on the ears. I have it on vinyl but it is available on CD.
[size=small]Allison Krauss & Union Station - So Long So Wrong[/size]
While her live album gets a lot of attention this recording actually has a
slightly better and more consistent lineup of songs, and it was produced
in a recording studio so the sound quality is better to boot. I have
the 180g vinyl LP Mobile Fidelity 2 LP set, but again this out on CD.
[size=small]John Fahey - The Transfiguration of Blind Joe Death[/size]
John Fahey wasn't folk music. He wasn't bluegrass. And he wasn't blues.
But there are hints of each of these genres to be found throughout his
music. He best described his brand of music as "American Primitive," which
I think fits pretty well. Very beautifuly played using a three-finger picking
style that he helped to pioneer, there are also a few tracks playing slide
guitar as well. Essential listening for anyone who likes acoustic guitar.