I can't remember if Undismayed has linked to this site before, but even if so, they keep adding to it so it is worth a return. You spend some time viewing these films..

Folkstreams » The Best of American Folklore Films

There are free streamed versions of very many documentaries on American folk culture and music, many of them quite good (several Les Blank films for instance). The picture quality is ok or worse, so filmicly this wouldn't be your site. But the main thing is the accessibility. And in the music films (most of them) the music is what matters anyway. I've been letting them run as I have been writing stuff and it is one of those times when you think: holy shit, I will never catch up.

Old time, blues, and Cajun music seem to be the most represented, with the Southern Appalachians definitely a focus of many of the films. But not exclusively, for instance there is "Every Island has its Own Songs: The Tsimouris Family of Tarpon Springs" about Greek music in Florida, one on Klezmer, on on a sideshow midget, and so on. It is worth your time just to see the old woman buckdancing while playing the harmonica in the middle of 'Talking Feet".

And need I mention the original D. Ray White footage?? Which is incredible to watch since he also has the gift of the gab (and 52 more steps, of course).