Here are some food links:
http://www.dogfoodanalysis.com/dog_food_reviews/index.php
http://www.dogaware.com/dogfeeding.html
http://www.dogfoodproject.com/
PetCo carries 3 quality foods - Nutro Ultra (NOT Natural Choice or Max), Natural balance, and Solid Gold. Nutro Ultra is very overpriced in comparison to the other two foods. I fed Natural Balance for a long time and love it. The Ultra Premium is great and all level - no need for puppy food.
PetsMart carries 2 quality foods - Nutro Ultra and Blue Buffalo. Again, Ultra is overpriced.
Anything else from either store is not quality food.
If you can find local feed stores or local pet shops, that is your best bet. They usually carry the best brands. CA Natural is a good food, by the same people that make Innova, and it's more affordable than Nutro Ulta and about the same price as Natural Balance and Solid Gold. When you do some research, just go to the store locator on the brand websites for info on where to find it near you. I have discovered some great independently owned pet stores because I was looking for local suppliers. The local stores also seem to know their stuff, which is nice!
ALL the quality foods are cheaper than Science Diet and usually cheaper than Iams/Purina/Eukanuba. You feed less of a quality food so the price evens out.
All that now said, I am currently feeding Costco's Kirkland brand. GREAT ingredients, it's made by Diamond pet foods who also makes Chicken Soup (also great food) and it's so disgustingly cheap it's laughable. I switched from CA Natural and Natural Balance to Costco's brand due to $$$. I pay $15.50 for 40 POUNDS of chicken and rice. Is it the very best food? No, but for the money it's far superior to low quality foods like Iams and Science Diet. For less than half the price! We've been thrilled with it and both boys love it - I am feeding the same amount of that as I fed of the Natural Balance and CA Natural because it's high quality.
So that's another option =)
I like to switch the foods around every 6-8 months or so - there are varying opinions on that. Food companies will tell you not to do that of course because they want your lifelong devotion and business =) Since there is no perfect food and they depend almost solely on kibble for their nutrition, I feel better switching it up every once in awhile to ensure they are getting a well balanced diet. I also think they enjoy having variety. I do not, however, switch them to foods with a major protein source change because I want to have options if either one of them ever needs an allergy formula. even sticking with the same basic sources of protein, there are tons of good foods out there to try. If your dog has a sensitive tummy, I would find something good and stick with it. Neither one of my do, thankfully.
That was way more than you asked for - Good luck!