completely alienne mentioned, in a comment about her de-cluttering activities, that she'd used an online book swap. She didn't mention her site, but there are many, ranging from international (Book Mooch) to country-specific, like the UK's Read It Swap It.
Strictly speaking, this might not de-clutter, since another book is coming to you, but it's a great way to read to your heart's content without the time limit of a library book. Or you could swap your book for one a friend would enjoy, recycling your book into a gift.
Bartering is on the rise as a way to reduce, recycle, or just participate in a community of support. People willing to propose barter discover, as Michael Phillips and Salli Rasberry said in "The Seven Laws of Money", "there are worlds without money".
U-exchange.com, a member-only site based in Cambridge, MA, includes boards for many countries. They've nearly doubled in the past year, with nearly 50,000 persons enrolled.
Some members have very specific requests: a pure bred Arabian horse for a Dodge pickup, for example. Other offerings hint at untold stories: "Boxes and boxes of legal paper for letter paper."
I'm considering a house-swap for a one or two-week vacation, one of the most popular and successful forms of barter; have you ever done it?
Barter offers are posted daily on Craigslist- see "For Sale/Barter" and "Housing Swap" listings.
You can also just plain give stuff away. We used the local board of the the Freecycle Network to give some unused office equipment to a young woman who needed it- as their website says, "changing the world one gift at a time."
I'm eager to hear of anyone's experience with barter or gifting.