Here's an offer from Black's Photo! With this Print+ Card you'll get 100 free 4x6 prints when you preload 100 prints on your card. So you'll have to pay for the prints in advance, but you'll be getting 200 for the price of 100!
The Print+ Card is available on this page and the 100 plus 100 free card costs $29.99. This offer is available through August 14 only.