Right after blogging about how to throw a clothing swap I discovered a great story on Shoestring Magazine with quickie reviews of four stuff-swapping sites, including Swaptree, Freepeats, Zwaggle, and Freecycle.
Each site has a different MO but basically you list stuff you want to give away and others come get it. Some sites charge for shipping and take a handling fee to cover costs. Others target major metro areas. Get a quick introduction to all four sites!