LibraryThing is a site that claims to catalogue your personal book collection. In practice, it's not very comprehensive, partly because it's hoping users will provide cataloguing information (like a wiki). Still, it works if you want a place to list all the books you own but don't have the time or skills to do it in Excel or Access. Also lets you share your collection with others as a way of social networking ("You've read jPod? So have I!").
