Though our big black lab looks very healthy, he has a rather sensitive digestive system and had on-going problems until Natural Balance was recommended to us. He doesn't tolerate anything with rice in it, so we tried the fish and potato Natural Balance, and he's been on it for several years now with no problems. Yes, it's a bit expensive, but PetCo (which is the only store I know that carries it) has a nice program of getting a free bag after every 10 purchases.
Natural Balance Ultra Premium Formula Dry is recommended by vwebb37