Delicious Library - Delicious Library 3: Catalog your books, movies, music, software, toys, tools, electronics, & video games. Archive your life.
LibraryThing - A home for your books.
BookPedia - Whether books line every wall of your house or barely fill one shelf, Bookpedia is the perfect...
Tellico - Tellico is a KDE application for organizing your collections.
Goodreads - See what your friends are reading.
Book Catalogue - This is a simple book catalogue application, to store a list of your books.