First, there's SwapTree, where you can obtain free books, DVDs, music, and video games from others by offering things of your own to swap. And while the word "swap" may conjure up an image of a two-way exchange, a more sophisticated "swap" might look more like this: Bradley receives a book from Max, who receives a CD from Reggie, who receives a DVD from Susan, who receives a video game from Bradley, and so on. With SwapTree, you enter information about items you have to offer, and click on items you'd like to receive, and you are then presented with a list of all the items you could potentially receive in exchange. When a swap is confirmed, SwapTree sends you a mailing label with the recipient's address and pre-calculated postage (which can be quite cheap using the media mail rate). You don't even have to go to the Post Office. In the meantime, you wait for your new goodies to arrive.
Another potentially useful website, in beta stages of development, is Lend Around. This is a system to allow you to lend items to friends, keep track of where they are, and easily find out what your friends have that you can borrow. Right now, LendAround members can lend and borrow DVDs, but it sounds like there's plan for expanding the categories of borrowed items.
What I'd love to see is a website where neighbors or friends can create a network and post all types of household items they own and are willing loan to others. This could include tools, appliances, electronics, sporting equipment, and so on. It could even include immobile items, such as a hot tub. The owner of the hot tub could indicate when they are willing to let others use the tub, and people could schedule use of it with the website. If you know of such a site or are planning on starting one of your own, I'd love to hear about it: you can email me at sharing (at) janelleorsi (dot) com.