http://www.dogfoodananalysis.com is not a bad place to start. But it has some biases that I think don't make it completely reliable. For example, some of its top rated foods (Orijen for example) are far too high in protein for many dogs, unless they are working dogs that expend a lot of energy every day. these foods made my dogs quite sick with intestinal upsets. I settled with California Natural which is a high quality food made by a good company with a good reputation, but is lower in protein and does not make my dogs sick as the higher protein foods do. It's not rated as high, but I think there is some bias to the site, so just take the information as a basic guide and go from there.

Avoid foods with soy, wheat, corn, byproducts and additives and preservatives, don't buy anything from a grocery store and you'll be off to a good start. Find a good small pet store (that does not sell dogs or cats) and ask lots of questions about the products relative to your dog's health, age, general condition and lifestyle.
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