Other sites (the first two are at American Memory):

Inventing Entertainment: The Motion Pictures and Sound Recordings of the Edison Company (Click on "Sound Recordings", with interesting articles on Edison cylinder phonograph and disc phonograph)

Emile Berliner and the Birth of the Recording Industry (Click on "Recordings")

American Pop: An Audio History -- From Minstrel to Mojo: On Record, 1893-1946 (with sound clips)

~Masato