Today's daily double deal at Ebates is for 16% cash back at Shutterfly. Also Shutterfly is having an extended Labor Day sale which is good through Sept. 7th. If you combine the two you can get some pretty good discounts.
Make sure to shop around at other sites before you buy. The companies that do photo printing seem to have some sort of revolving sales deal all the time. I can't say if Shutterfly has reasonable prices to begin with. For example their photo mugs are on sale for 25% off which makes them $10.49 but over at Vista print they have photo mugs for 50% off for $7.49 so the Vistaprint sale is cheaper today even with the 16% cash back.
To get the cash back you need to be signed up with Ebates. Then simply go through the Ebates site before you start your shopping. I also get a referral bonus if you use my links to sign up with Ebates.