Even if you can't or don't want to sell something, it's likely that you can give it away. Put it in your yard with a free sign on it or try Freecycle. The Freecycle Network is a collection of almost 3,000 local on-line communities totaling over 1.5 million people. You can offer free things to the community, or even request an item you would like to have. Even simple things like sharing your old magazines with co-workers or neighbors can make a difference.
Building and construction materials can also be reused by charitable organizations such as Habitat for Humanity. They operate a number of Re-Stores that sell materials donated by retailers, manufacturers, and homeowners. Proceeds help Habitat for Humanity to build or rehabilitate homes for their clients.