Go here and if you don't already have a Walgreen's photo account go ahead and sign up.
After you've signed up/signed in click the gifts link, and from there (on the left side of the screen) pick the Collage option.
Go ahead and create your 8x10 collage print and when you check out enter the coupon code CLG8X10 to get it for free. Then select to have it picked up at your local store to save on shipping!
This code is good until 10/22