Maybe I've been in college too long, but I've grown to love used books. It's gotten to the point where a brand new book just makes me plain uncomfortable. Same goes for CDs.
I also enjoy donating or selling off things that I no longer want anymore. It's nice to feel that my unwanted possessions are now being enjoyed by someone else, and that I've chosen to surround myself only with things I truly treasure.
In general, I'm of the view that posessions, much like natural resources and money, need to flow in order to do the most good in the world.
Swap Tree is a website that facilitates the flow of posessions--you post a list of books, CDs, DVDs and games that you don't want anymore, as well as a list of things you'd like to acquire. Everyone else does the same. The website helps arrange favorable trades among users (one item for one item), and the users involved can decide whether or not the trade is acceptable. If the trade is accepted by all parties involved, the users ship their items to one another. The only fee is the cost to ship your item to another user.
Users on Swap Tree are held accountable by a system in which users can rate the reliability of other users. Shipping deadines are strict--once a trade is accepted by all parties, each individual is required to ship their items the following day.
I've mostly been bartering the 90's pop music I no longer like for the 90's pop music I am no longer ashamed to admit that I do like.