This resources has been available since last November, but I just stumbled across it today and had to share. When you have some time to devote to browsing, check out the Cylinder Preservation and Digitization Project  from the Department of Special Collections at the University of California, Santa Barbara. From their website:
Cylinder recordings, the first commercially produced sound recordings, are a snapshot of musical and popular culture in the decades around the turn of the 20th century. They have long held the fascination of collectors and have presented challenges for playback and preservation by archives and collectors alike.
With funding from the Institute of Museum and Library Services, the UCSB Libraries have created a digital collection of over 6,000 cylinder recordings held by the Department of Special Collections. In an effort to bring these recordings to a wider audience, they can be freely downloaded or streamed online.
You can search the collection by keyword, or browse by performer (the sort is on FIRST name), title, isue, or year of release then play or download the files in MP3, Quicktime, or WAV formats. Pretty fun stuff! I searched for "roosevelt" and found three recordings of Theodore Roosevelt's voice! How cool is that? Check out this page  for information on the history of cylinder recordings.