Truckin' My Blues Away is an hour long audio documentary on older Southern blues singers featuring Little Freddie King, Captain Luke, and others. It promotes the work of the Music Maker Relief Foundation which supports traditional musicians (previously). There is an accompanying slide show and the producers are working on another documentary, Still Singing the Blues.
Whole Lotta Shakin' - a PRI documentary series on the history of rockabilly, hosted by Rosie Flores.
So You Think You Hate Country Music? Then listen to this. The roots of American country music may surprise you. In this series of NPR programs, trace the gradual development of real country music through the first half of the 20th century. Learn how a woman's instrument of the late 1800s, the parlor guitar, became the the central symbol of country and rock; see how African-American musical forms like gospel and blues meshed with the development of country and early rock and influenced the traditional forms in turn; listen to German-Mexican hybrids of accordian style; find out why women had so many honky-tonk torch songs to sing in the late 40s. The series contains hours of content (narrative, interviews, music tracks), and a multitude of excellent links for deeper digging.
Boosting the Blues covered on Marketplace Radio. At the bottom of the page is a short summary and a link to the David Brancaccio interview (12 minutes or so in Real Audio clip) of Taj Mahal's involvement and spreading the word about the Music Maker Relief Foundation.