Also on live365 - Sugar in the Gourd & The Lost Anthology.

WFMU has a live stream, and basically all their shows archived so that you can listen to them in a stream whenever you like. Check out especially The Radio Thrift Shop . The Secret Museum of the Air is also an outstanding show, and if you look through the archive titles you'll be able to see which shows feature the sorts of music you are looking for. The Shrunken Planet is dedicated to folk. (This program was referenced in the famous Jean Ritchie "The World is Old Tonight" thread - he played it awhile back.) One of Doug Schulkind's shows was "The Alan Lomax Special". You can find it on the special archive page.

WKCR doesn't archive their shows, but do stream their broadcast. Check out their "American" & "Jazz" programs.

The Red Hot Jazz Archive has the films St. Louis Blues & Symphony in Black up on their site, as well as assorted individual songs.