This is perhaps the best online resource regarding dog foods (IMO) because they are completely unbiased and base the ratings solely on the ingredients -- not only quality of, but species-appropriateness as well.
http://www.dogfoodanalysis.com/dog_food_reviews/They also explain the ingredients "in plain English", so be sure to scroll down for their insightful, fact-based write-up for each food.
Not coincidentally, the most "well-known" mainstream foods can be found easily in the "one star" tier -- complete with thorough explanations of why they're there.