There’s a ton of good work being done in libraryland with mashups and bibliographic data (I’m looking at you, LibraryWebChic!). But for user experience and overall awesome, I love this mashup by John Herren of just the New York Times bestseller list and Amazon APIs:
He detailed how he did it in this great blog post, and it set my mind to racing with possibilities for libraries. For one, I didn’t know that the NYT bestseller list had an API! Public libraries all over should be leveraging this on their websites, with links to their holdings.