Timothy Spalding has put together a really interesting site, called LibraryThing, that lets you list your books, tag them, and share the list with others. You can search by bibliographic info, user or tags. And Tim does some useful listing of the top 25 books by author, tags, etc.
One of the cool things: You enter a book into your list by typing in sloppy information. For example, if you want to enter The Social Construction of What? by Ian Hacking, you can type in “social construction hacking” and LibraryThing will search the Library of Congress and Amazon. Sure enough, it finds the right one. Click and all the bibliographic info, plus the cover graphic, are added to your list.
It’s basically free, although to add more than 200 books to your list, Tim asks for a one-time fee of $10, which seems pretty reasonable to me…especially once Tim adds RSS feeds so we can subscribe to a tag, reader, etc., and discover the new books others are reading.