I get most of my pet food from either PetFoodDirect and PetCo.
I get coupons from both, but with PetCo they usually don't do free shipping or percentages off of food and litter although they often have some good prices. PetFoodDirect can sometimes be higher priced, but with their coupons it will often give you enough savings to cover the cost of shipping and more.
With either one, even though I get their coupons in email, I still google because there are often more and better ones out there if what I have doesn't suit me at the time.
Oh Yeah... PetFoodDirect carries most of the high quality foods one could want.