Some sets I have and like include Louis Jordan's LET THE GOOD TIMES ROLL (lots of good songs that don't show up on the various anthologies and compilations), Nellie Lutcher's AND HER RHYTHM, Julia Lee's KANSAS CITY STAR (some Benny Carter/KC jazz on that set), and the NASHVILLE JUMPS collection, which documents the Nashville indie R & B scene from 1945-55. Some surprising jazz cameos on that one from the likes of John Coltrane and Phineas Newborn, among others.
For those interested in the American left, SONGS FOR POLITICAL ACTION is an intriguing set, although some of the music leaves a little to be desired. It contains the complete Almanac Singers recordings. Only problem with Bear Family is that they're really pricey; I picked all of these up when I worked at Borders and could get a good discount. There's one online site that has most of these for prices that average out to about $16 or $17 a disc--I'll see if I can find the link. The set I'm hoping to get next is Piano Red's DR. FEELGOOD.
The Carter Family is a monster, but the sound's better than the Rounder re-issues, and Charles Wolfe, who's at work on a bio of the Carters, wrote good liner notes for the book.