I received an email about Swaptree a couple of days ago. It's a swapping service for you to swap books, CDs, video games and DVDs. There is no joining fee and you only pay the postage for the swap. It looks good to me but I can't try it as it looks like it's an America only service. If you do check it out and it's as good as it looks, or if it's not as good as promised, please let me know. Hopefully it will help you save a few dollars by swapping instead of buying.
You can check it out here and here.