Bookies
Here's a pretty nifty service: PaperBackSwap . They have over 800,000 books listed. How it works is that you initially list at least 9 books you have that you want to trade to start and they give you 3 credits. Each credit is worth one book. When somebody orders one of your books, you send it directly to them and you get another credit (you pay the postage.) Whenever you want a book, you spend one of your credits to get any book in their listing (you don't pay postage.) Kinda cool this collaborative stuff. PBS also generates a mailer for you to slap on your book detailing the exact postage you need (it knows from the ISBN), so you just put on the stamps and put it in the mailbox. No trips to the post-office. So basically, for the price of media-mail (which is pretty dang cheap) you can upgrade any of your books to others that you like better. This really beats the used book stores which typically give you 25% of the value and then charge at least 50% for any book you want to bu...