CVS is offering a free 8x10 enlargement through their website. Use the code FREE8X10 and select in store pick up for an absolutely free 8x10.
If you haven't already signed up for their online photo with your CVS card you will also get free prints.
Shutterfly is running a deal where if you create your own photo blog site and share it with your friends they will credit you and your friends(if they have an account) with free 4x6 photos. I recently received 40 free prints doing this. Now I'm going to wait for a great deal on shipping to save even more!