The RailsEnvy guys have just launched their new Envy Casts site which is powered by Spree. The site allows you to purchase screencasts and is an excellent example of how one can sell downloadable content using Spree.
The site uses a few new Spree extensions including the Paypal Website Standard Extension. Envycasts also uses an extension to support downloadable content through Amazon’s S3 service. If anyone is interested in turning that code into an official extension just give those dudes a shout and I’m sure they’d be happy to provide the code.