For many years I have been a customer of Collectors' Choice Music, which started out as a seller of re-issues but has since evolved into one of the major players in licensing stuff to release under their own label. Some of their own reissue efforts have been forgettable (such as their ill-fated reissue of the simply horrible Don Ho Christmas album), but their latest catalog has a ton of great stuff.
Some examples:
In the CC "exclusive" category, they have the 3 1980s albums Mel Tillis did for Elektra, the first two 1961 albums by comedian/social activist Dick Gregory, a twofer from the 1960s by rockabilly legend Ronnie Hawkins (with "The Hawks", later to become The Band, backing him up), and one I had never heard of, Ginger Baker and the DJQ2O, a jazz album by the drummer for "The Cream".
CCM also is running a music DVD blow-out, with a lot of stuff on sale, and they also feature some other interesting new releases, including two CDs of commercials from the 1950s and 1960s done by rock and roll performers, a new import with the Capitol albums done by some former Byrds named McGuinn, Clark and Hillman, and even the new Bear Family reissue of Merle Haggard's Capitol Records recordings from 1968 thru 1976. The latter includes his epic 1970 Bob Wills tribute album, which reunited many of the original Texas Playboys.
Be sure you have a lot of money! Their website (which I have always had trouble with, but I assume that's because I am on a dialup ISP) is...
http://www.ccmusic.com/