The Google Book Search Book Viewability API enables developers to: Link to Books, thumbnails, and previews; Know whether Google Book Search has a specific title and what the viewability of that title is.
Additional book-related API's:

BookMooch API

ISBNdb API

O'Reilly Safari API

Provider: Google Code	Submitted By: APIFinder.com Staff
License: Open (free)	Email: Email this contributor
Price: 0	Connection Protocols: Other
Notes:
Functions: Search
Languages/OS: Web Service, Scripting Language