Hello there! I work at a Holistic dog bakery and food carrier so I fancy myself sort of a "specialist" in the area of canine diet.
My suggestion: AVOID grains. While they are not necessarily harmful they definitely don't contribute anything specifically wonderful to the diet.
There are great goods that are grain free. My two suggestions are to look into Innova's EVO line. It's my favorite food; totally grain free and outstanding protein/fat. My Shango eats it and it's done wonders for him; skin/coat, weight control, and productive energy.
Also, Solid Gold's Barking At the Moon is a great food to look into that not many people know about. The price is fairly reasonable whereas Evo gets a bit expensive.
Overall, holistic (no wheat, corn, soy, by-products) is the way to go. Let me know if you have any specific questions.