Some dogs can have allergies associated with the protein source and corn products. They tend to develop allergies to the more common protein sources, so Salmon is a good direction to go in. There's also Venison, Duck (kinda greasy), and even Kangaroo!
As far as getting away from corn, some foods use rice.
Whatever you do, stay away from Nature's Recipe or anything made by Heinz. I don't like the way they handle their foods from the plant to the retailer.
Hills, Eukanuba, and Purina all have very good handling policies and great prescription diets.