I have clients ask from time to time about selling things they are ready to part with. This article I discovered on Man VS. Debt is a good explanation of the various ways and places you can sell, and the difference between them.
Here's another great article that shares selling tips and directions for Ebay, Craigslist, and Facebook!
Another great resource to check out is thredUP, an online consignment store. A good friend of mine recommended it.