I am sure that you know about Google Books: http://books.google.com/
Even if I truly believe that Google wants the good by publishing all this information for free - We all remember the sentence: "Don't be evil" that is part of the Google code of Conduct-. I think it is not a good idea to have only one service that provide access to the "world culture"... Competition is always good for consumer...
The French National Library (BNF) and some other public libraries (Hungarian, Portugal) have created a new site to offer a similar service in beta: http://www.europeana.eu. It is true that currently the list of books is really small compare to Google but I am inviting you to use both of then.