ISBN database

ISBNdb.com's remote access application programming interface (API) is designed to allow other websites and standalone applications use the vast collection of data collected by ISBNdb.com since 2003. As of this writing, in July 2005, the data includes nearly 1,800,000 books; almost 3,000,000 million library records; close to a million subjects; hundreds of thousands of author and publisher records parsed out of library data; more than 10,000,000 records of actual and historic prices.
More information: http://isbndb.com/api/v2/docs