Simply put: you can buy stuff from Auctions and sell them.
Especially computers, laptops, monitors etc.
you could sell them at your neighborhood flea market if there is one.
Try auctions like
http://www.govdeals.com/index.cfmhttp://www.liquidation.com/(moreover, you can also buy used supplies from the govdeals.com website, like printers, and industrial products etc)
*a note about govdeals.... you have to pick up the items from their locations, so buy locally or near enough that you can transport them
