SwapThing API

From their site: SwapThing is a community of users who want to swap, buy and sell things in a new way. The purpose of the SwapThing Open API is to share data and increase the opportunities to swap. Our API is built in simple HTTP_XML so everyone can use it. The API provides two basic sets of functionality: Tag Searches - Give us a tag and we'll give you a feed of item data. Choose how you want to use and format it.
Item Details - If you are not using all the data from the feed and have a request for more info on a specific item, you can send us the Item ID from the original feed and we will return the data on that item.