I used Iris Dement's My Life album as source material at one CES Vegas. Sounded great on Crosby-modified QUAD 63's. Stuart Duncan, a great fiddle player, is one of the superb musicians on the album.
Chris Hillman's (The Byrds bassist) albums on Sugar Hill records possess great sound quality, and are musically great (a nice "bonus" ;-), His albums as a member of The Desert Rose Band as fantastic as well. His latest album was produced by Mike Campbell of Petty's Heartbreakers.
T Bone Burnett's (producer of the O' Brother soundtrack, as well as The New Basement Tapes) Truth Decay album (originally on Takoma, a label known for good sound and artists) sounds REALLY good.
I'll think of some more if you want.