While learning about access to e-books and audiobooks I was amazed to see the variety of places to find them. I guess that is why Google is trying to do its best to "digitize" the world. It sure would be easier to go to one place to find out what's out there. The biggest difference that I see in many cases is that Google's books actually look like pages from the books, whereas many of these other e-books seem to be glorified pdf's.
On my train trip across the United States this summer I met a gentleman who was using an e-book reader very adeptly. He told me that he likes it better than lugging around big hard cover books. He is able to change the font and contrast to give him a reading experience that was better than "screen" reading. I don't know...it still didn't feel the same.
Librivox looks like a very promising site for audio books. Of course, it does depend on the quality of the reader as well. Another site I have used through our public library in Contra Costa County is Califa . It is a collection of both audio and e-books for libraries. I am sure many public libraries are probably already part of this consortium.
This whole area seems to be in its infancy, and it will be interesting to see how it develops with regard to school libraries.