Air conditioning units, from small window units to large commercial units can be sold to your local scrap yard.  You can sell the units whole, usually paid for the unit tonnage (ex. 1 ton, 1.5 ton, 2 ton..) or you can get money by breaking down the units.

First step is to have the freon removed professionally from the unit.  You can separate the copper wiring, copper tubing, the radiator, and the sealed unit (compressor) as well as the steel casing that remains.  By selling the materials separated, you should be able to get more money from the scrap yard than selling the units whole.  Although, your time should be considered as it is time consuming to break down the units.