More and more groups are popping up all the time to help you recycle the items you may be done with. Rehash, which is still in beta stage, allows you to swap books and clothes. It's kinda of like having a roommate with out having to share a bathroom with a total stranger.
It looks like college students also swap text books on the site. Fabulous! Textbooks always seem to be SO expensive!
Another great way to reuse with out causing the demand for new things to rise.