BookLamp offers an interesting and (ahem) novel idea when it comes to finding books.
Those familiar with Pandora know that it works by analyzing a musician or song that you like and making choices for new songs based on the artist, style, beat, and other musical elements. BookLamp seeks to do that, but with books. Through the analysis of things like writing style, word use, and the like, BookLamp tries to make recommendations for further based on similarities between the book you selected and other books within its database.
A video on their site explains everything in greater detail.
They've only got a few items in the database, but they're looking to grow... and hopefully have their idea purchased by Google.