Premium & Organic Dog Food and Dog Treats - Free Shipping often has good deals, free shipping, etc.
Pet Food Online | Dog & Cat Supplies & Products | PetFoodDirect.com is also a good one.
I would recommend Acana, Orijen, Now!/Go!, Fromm, Nature's Variety, Taste of the Wild.
My friends 4.5lb yorkie, Bandit, has a pretty sensitive stomach and used to have alot of digestive issues, and since starting Acana, he hasn't puked or had diarrhea or anything!