GoogleBooks is a Ruby wrapper that queries the Google API to search for publications in the Google Books repository. It is authored by Zean Tsoi and provides additional methods and search options. Queries return results, each with their own set of attributes that can be individually configured.
Innovation in web service APIs is not always technical, sometimes it's about money. Such is the case with Yahoo's announcement that later this year they will begin charging for usage of BOSS (Build your Own Search Service), their search web service for developers. Given that search revenue is typically ad-driven, and that advertising doesn't typically mesh with APIs, this has meant that search APIs have been one of the most challenging classes of APIs for providers to monetize. So it's notable to see how Yahoo has chosen to tackle this: via a 'utility' pricing model, somewhat akin to how infrastructure services like Amazon Web Services charge by usage.
Google has announced several very interesting updates to its Book Search tools, including an embeddable viewer for book previews and a data API. These should open-up a wide range of book-related applications. This follows-up on Google's release in March when they launched the first API for Google Book Search, the Book Viewability API.