These are links that I find meaningful personally. Check them out if you have the time and inclination. They are all appropriate for middle schoolers, though I do not personally believe or vouch for every single idea or viewpoint expressed on them.
Woody Guthrie Home Page: My musical hero. As Bob Dylan said, you can learn how to live by listening to his songs.
1) Max Hunter Folk Song Collection 2) Wolf Folklore Collection: Ozark Folksongs Many of the songs that I research and collect are found here. These are simple recordings from the Ozark mountains. If you want to know what part of America REALLY sounds like, listen to some of these songs. Lyrics are included.
American Memory / Library of Congress: This is simply one of the best sites out there for anyone who wants to explore what it means to be an American. The archives of the Library of Congress are packed full of countless historical sources, and many of them are accessible online through this site. You can see Civil War photographs, hear field recordings of old folk songs, see the printed pages of George Washington's diary, and SO MUCH MORE. Every American should spend a few hours a week just browsing this stuff. Just jump right in and see how long you can keep yourself interested.