Smithsonian Folkways has 24 hour-long podcasts giving and overview of the Folkways (and I think Library of Congress) music, oral history and poetry collections free for the download. You like Woodie Guthrie? You like Leadbelly? You like early jazz? It's all here and it's all free! Check it out: http://www.folkways.si.edu/explore_folkways/folkways_collection.aspx
I downloaded all of these yesterday and started burning them onto CD (what's an "iPod?"). I listened to the first one last night and started the second driving into work today. These first two are an interesting history of Folkways records and Moses Asch, with occasional music by Woodie Guthrie, Leadbelly, etc. These are worth listening to in part because they talk about how Asch ran a record company without any "stars," and in fact how "stars" cause problems for record companies. He had an very interesting way of thinking about things that would be useful for us in the Nation to consider.
I am really looking forward to the three segments on the Anthology of American Folk Music. Our local library had this set of six CDs, and it is really amazing and worth getting. The Asch recordings of Woodie Guthrie are on my christmas wish list.