Check out Canidae Platinum:

http://www.canidae.com/

I feed both my dogs the 'All life stages' formula and they do great on it. The Platinum is specially formulated for seniors and overweight dogs.

Andy

ETA: The meat meal that Canidae uses is not a rendering by-product, but actual human grade meal. There's no wheat or corn, and 3 out of the first 5 ingredients are meat.