sooner or later, someone will mention Jazz at the Pawnshop. personally, i think the music on it lies somewhere between mediocre and crappy, but the sound quality is something to write home about. i think it's for people who want to listen to their equipment.
If you can stretch yourself to the blues, definitely check out the DCC release, "Blues Hoot" by Lightnin' Hopkins. Raw, intimate, and beautiful acoustic guitar and harmonica with genuinely passionate vocals to boot. It's a wonderful way to test the clarity, resolution, and soundstage of your system, and the music is absolutely wonderful!
The C-Nuts - Blitzkreig Bop and Other Jazz Mutations Possibly the only good album from Mapeshade's catalog, The C-Nuts do jazz renditions of Pop-rock staples from 1979-1985. The material may only be so-so for some younger listeners who aren't familiar, but the recording quality is crap your pants good.
The Sultans Of Swing is really a standout track here. (normally a Dire Straights song)
While this strays somewhat from your intended genres, I love Sufjan and Califone and I also love Pinback. You should check them out. Not acoustic, but sparsely instrumented and amazingly produced. Check out "penelope" or "non-photo blue" for a good place to get started.