Coupons.com has a printable coupon good towards the purchase of the Shrek Forever After Blu-ray (both the BD/DVD combo and the BD editions, as well as Shrek: The Whole Story). To access it, go to the Coupons.com website, click on the "Entertainment" tab and the coupon will show up on the coupon display area. You will need special coupon printing software installed.
I just printed this out and below the coupon it states "Save $5.00 on any of these Shrek products"
It has listed the single dvd, single blu, blu-dvd combo, the whole story blu box, the whole story dvd box, and double dvd pack.