The LibraryThing Ruby SDK by Jason Wadsworth allows API interaction to access book catalog features, displaying covers based on ISBN numbers. Guides display how to access the API and interact with Ruby Gem.
If you're interested in developing maps mashups using the Yahoo! Maps API but have not yet had the chance to use those APIs, you're in luck. There's now a very good book to show you the way, Yahoo! Maps Mashups by Charles Freedman.