The Freecycle Network is a grassroots and entirely nonprofit movement of people who are giving stuff for free in their own towns. It is a effort to promote waste reduction. There is a separate group for each community that you can join.
Items for Sale at the Resource Center: The Resource Center is a Chicago-based nonprofit environmental education organization focused on demonstrating innovative techniques for recycling and reusing urban materials.
Article with advice for artists on how to set a price and claim bartered goods and services. This article is written by an arts business expert. Some of the art-specific examples may be less than contemporary, but the business principles that are discussed are excellent.