The Good Guide's mobile app. allows you to scan in a bar code from a product and see ratings in terms of its health, social, and environmental impact. http://www.goodguide.com/ Although the website only links to the iPhone app it is also available in the Android store. The app. is free for both platforms. How does sweetened fizzy clear water weigh in on Good Guide (I can hear the "take back the tappers" cringing but it was the only thing with a bar code in arms reach)? Pretty bad on health but above avg. on environment and society. Submenus allow you to see fine level breakdowns.
It does take a looooong while to install all the product data and I haven't tried it out at the grocery store yet but if you are looking to justify that purchase (or justify not purchasing!) have a look at the Good Guide rating first.