Grocery IQ does that and more. You can even track what coupons you have loaded on your shopper card and pair those with prices/sales in your particular store! How cool is that?
Sadly, I do not have an iPhone or iTouch, but for those of you who do, this app could be quite helpful. Check out this link for detailed information about all this app can do then click over to iTunes to get it for FREE for the month of April!
Let me know if you get this app and what you think of it!