Books is a free tool that can help you organize your book collection, acting as a sort of iTunes for physical books. This virtual card catalog lets you classify all the books you own using pre-defined fields like title, author, and publication date. You can also create your own.
Books also lets you track and store summaries, cover images, personal reviews and ratings, notes on multiple copies of a single book, and more--and it even helps you track a books lending history. Smart Lists, much like iTunes' Smart Playlists, let you group books by criteria--for example, by author, genre, or publication period. Books also imports another great feature from the music world: the online database. Using Web sites such as Amazon.com, Books can "quickfill" fields. Type in the ISBN for any tome and Books will auto-fill much of the books metadata and even pull in a cover image.
Books also gives you export options in case you want to use your book list elsewhere, letting you export into HTML, PDF, onto your iPod, or even just as tab-delimited text, in case you want to drop it all into Excel. In addition to being free, Books is also open-source so that means if you're a developer, the sky is the limit for tweaking Books and creating localizations and custom plug-ins. It also means a lot of users have pitched in to help Books' conscientious and responsive developer, giving this tool a life beyond what it might have otherwise.