Cory Doctorow posted "Old time record enthusiast rips and posts thousands of 78RPM tracks" on BoingBoing today that points to a collection of 78s on the net. One of the commenter's of the post pointed to the "Cylinder Preservation and Digitization Pilot Project" (CPDPP) that UCSB runs since 2002. The CPDPP has about 8,000 archived and available for download.
One feature on the site that I have been checking out is the various streams of recordings. For instance, you can get "Historical Speeches on Cylinder", "Pioneers of Audio Theater" or "Popular Songs of World War I". I have been glued to listening to "Operatic Cylinders from the William R. Moran Collection".
I doubt that these streams will give SomaFM a run for the money, but it is certainly worth checking out.