I think this is a trend that is starting to pick-up (or at least I hope it is) — stores offering discounts or incentives when you donate used goods.
Two major retailers offering a good program:
Bring in an empty used container from their products to recycle and receive free new products in return. The more you bring in the larger your gift becomes. Bring in 3 empty containers and get a tube of lip gloss, or bring it 10 containers and you get to pick out any product (less that $25) for free.
Visit a Timberland store to donate a used pair of shoes and you'll get 10% off a new pair of Timberlands. Timberland is partnering with Soles4Souls, who donates shoes to those who need them.