The increasing popularity of social networking web sites associated with book collectors prompts us to share the following list of sites you might want to investigate, if you've got more books than you know what to do with (and you don't want to donate them to the library!):
BookCrossing -- read, write a review, then leave your books for others to find, either at random locations or any of a network of pre-established "Crossing Zones". Then, via a bookplate label with an identifying number and the web address of BookCrossing, you can encourage other readers to go online and leave comments about your book...and help you track its travels worldwide.
PaperbackBookSwap -- join other readers who share books (both paperback and hardback) with one another, just for the cost of postage.
BookMooch -- set up a list of books you want, post a list of books you have, then trade with others.
What'sOnMyBookshelf? -- similar to BookMooch, plus "tag" the books in your collection to assist you in connecting with other readers with similar interests.
Bookins -- Make your books available and find other people's books, all for a flat-rate postal delivery fee.
What do you think about any of these...or do you have some other favorites to share?