Accumulation Rule

You only use 80% of your personal belongings. So the new rule is, if something comes into the house then something must go out.
There are a variety of websites available to help you get rid of perfectly good items that you no longer want or use- freecycle.com is one that comes to mind. You can join a "chapter" near you to give away those items to someone that needs and wants them. They also have spinoff sites that you can advertise items for sale (tag sale), barter for services or adopt pets.
Besides the obvious EBay and Craig's List to sell your unwanted items how about trying a consignment shop? There are also local charities and the Salvation Army if you just want to get these things out of the house with no further hassle. Could a friend or family member use this item?
One thing you have to accept is that yes, you paid good money for this item. But, you are not going to get what you think it may be worth so just let it go.... It's out of the house and someone is making use of it.