Dave McKay posted to the Raspberry Pi community about this topic with great resources.
Google API for ISBN is accessable @ https://www.googleapis.com/books/v1/volumes?q=isbn:007024572X. Substitute your book’s number for the last 10 characters.
UPC lookup’s are free at the UPC Database. There is a limit on free access and most of the data is user entered so I wouldn’t count on it for running a business but it is great fro personal use. I even added a code for an item I had handy.
Paul Hutchinson's Blog 