Cambodia: Traditional Music Vol. 1 (released 1975) and Cambodian Cassette Archives: Khmer Folk and Pop Music Vol. 1 (released 2004). I'm not too enamored of the traditional Cambodian music, but the second disc, a recording of Cambodian garage bands, rocks most mightily.
Casual Victim Pile: Austin 2010. An excellent compilation of Austin music curated by Gerard Cosley with the extraordinary Follow That Bird! (who have re-formed as Mirror Travel) and the great Distant Seconds.
Chains And Black Exhaust (released 2002). This top-notch comp collects rare psychedelic funk tunes.
Chess Psychedelic Jazz and Funky Grooves (1968-75) and Chess Soul: A Decade of Chicago's Finest (1963-72). The former collects the awkward attempts of some great jazz, blues, and soul artists to make garage-y psychedelic music. Perhaps it helped create a market for the brilliance of the Chains and Black Exhaust music, but it pretty well sucks. The latter collects the more classic Chess blues, soul, and R&B music, and it is solid.
Classic Bluegrass from Smithsonian Folkways (released 2002), Classic Harmonica Blues From Smithsonian Folkways (released 2013), and Classic Mountain Songs From Smithsonian Folkways (released 2002). Smithsonian Folkways is doing the lord's work here. Each of these collections contains amazing old music that would be right at home on Harry Smith's Anthologies of American Folk Music (and, in a couple of places, overlaps that collection). The Harmonica Blues compilation came out last year and is proof that Smithsonian Folkways can continue to curate a collection built around a central concept, and the label's seemingly endless depths and quality of their archives, a veritable diamond mine of folk music.
CMJ 2007: The Bands, The Music, The City, Vol. 1. A freebie collection of indie rock bands from 2007 that I will probably delete.
The Complete Stax-Volt Singles 1959-1968, The Complete Stax-Volt Singles Vol. 2: 1968-1971, and The Complete Stax-Volt Singles Vol. 3: 1972-1975. Total songs on these three boxes: 669. The first two box sets are perfect. The last still has moments of brilliance, but things were getting sloppy at Stax-Volt.
Country Funk 1969-75, Country Got Soul Vol. 1 (rel. 2003) and Country Got Soul Vol. 2 (rel. 2004). These are much better attempts at fusing two genres than the Chess Psychedelic stuff. The tracks are well-selected from white folks (especially Memphis-based white folk) who were often classified as country musicians while any fool can hear how much R&B goes into their sound (Charlie Rich, Dan Penn, and Bobbie Gentry, most prominently).
Country Legends Hits (1955-75). This is an 8-song cheapo compilation that I may have bought in a gas station with some truly excellent songs - all original versions! - on it: Glen Campbell's "Rhinestone Cowboy," Conway Twitty's "Hello Darlin'," Sonny James' "Young Love," Ferlin Husky's "Wings of a Dove," Merle Haggard's "Okie from Muskogee," Tennessee Ernie Ford's "Sixteen Tons," Faron Young's "Hello Walls," and Willie Nelson's "Crazy." I think I bought this on a road trip in 1991 or 92 and realized that I really love country music.
Crossing Jordan Soundtrack (rel. 2001). This is a show I never watched, but I had the distinct impression that it was not one I would enjoy. However, this soundtrack, which is mostly Americana types covering iconic 60's songs quite well, leaps way higher than I could expect with Vic Chesnutt's "Buckets of Rain" and - especially - Richard Thompson burning down "Season of the Witch."