Okay, I should be more clear on this one.  The recordings on Smithsonian Folkways are not free to download, but once you pay a couple of bucks to download them you can use them for free in your classes for educational uses without having to worry about any licensing or copyright issues.  For more information on this topic consult the Smithsonian Folkways Copyright page.  The Smithsonian Folkways site has thousands of music and spoken word tracks from recent history as well as back to the dawn of the use of wax cylinder recordings. This makes the site ideal for music educators and people who are just trying to find that unique, or eclectic old song that they can’t find anywhere else.  The tracks on Smithsonian Folkways go back do the dawn of the 20th century (early 1900’s for those of you not wearing your thinking caps today), and all have been remastered and made available to preview in streaming audio format.