Here are some ways to profit on empty ink cartridges as well as do some good for the environment:
Sell on eBay - I recenlty sold 5 empty *virgin ink cartridges for $12 - a little over $2 a piece for each cartridge.
Recycle at Staples, Office Depot or Office Max and get a $2- $3 store credit for each ink cartridge you bring in for recycling. These programs you usually have to wait until the next month in order to get your rewards certificate to use.
Check out Empties for Cash where you can send in your ink cartridges and they will send you a check. They even pay for your postage! There is a price list on the site that shows what your cartridges are worth. Prices range from $.25 - $4.00. Lexmark brings top dollar with $4.00 per cartridge on specific cartridges.