I purchased a Sony PRS-600 Digital Book reader for my daughter for Christmas. I could not get the Sony Reader software to load onto my machine and was just about to return to the store. I noticed in my research that Adobe Digital Book reader was compatible – it works and synchronizes with the Sony PRS-600 reader.
Does anyone recommend an ebook commerce site that is compatible and friendly with Adobe Digital Edition application?
http://ebooks.addall.com provides a good price search across a whole bunch of stores.
http://www.feedbooks.com provides nicely formatted public domain books.
The rest really depends upon what you like. For instance I'm into SciFi, so I make heavy use of the Baen store: http://www.webscriptions.net
One final note: The Amazon and Barnes & Noble stores are not compatible with your Sony 600, although the B&N store may be compatible later (once Sony issues a firmware update).