Our trainer,
Liz Palika who has written several books on dog nutrition, recommends high quality foods with no grains. Her top choice is The Honest Kitchen (a dehydrated raw food) but it's extremely pricey, especially for those of us with large dogs. Her next choices were Wellness CORE and the other one has left my mind at the moment.... Sorry. We used CORE for awhile and the dogs did wonderful on it. We only switched because our vet was concerned about the high protein content (not that its all protein, the carbs just come from things like sweet potatoes and fruit instead of rice or corn) on our 10 year old shepherd's kidneys. Generally high protein content is desired, especially for young or active dogs. I still question her advice but I'm not taking any risks with my baby
We are now using Natural Balance Duck and Potato. It's also grain free but has a lower protein content, I think it's around 22% which is more average. That variety of Natural Balance was also on our trainers list of good foods, just a little further down.
Basically just look for a grain free, filler free food. That means no corn, barley, beet pulp, by-products, etc. The list of food ingredients should be relatively short and possibly followed by vitamins and minerals. For example...
Here is the list of ingredients from a Eukanuba food, which many people think is a "good" food:
Chicken, Chicken By-Product Meal, Corn Meal, Fish Meal (source of fish oil), Ground Whole Grain Sorghum, Chicken Fat (preserved with mixed Tocopherols, a source of Vitamin E, and Citric Acid), Brewers Rice, Dried Beet Pulp (sugar removed), Natural Chicken Flavor, Dried Egg Product, Brewers Dried Yeast, Salt, Potassium Chloride, Fructooligosaccharides, Vitamins (Vitamin E Supplement, Ascorbic Acid, Beta-Carotene, Vitamin A Acetate, Calcium Pantothenate, Biotin, Vitamin B12 Supplement, Thiamine Mononitrate (source of vitamin B1), Niacin, Riboflavin Supplement (source of vitamin B2), Inositol, Pyridoxine Hydrochloride (source of vitamin B6), Vitamin D3 Supplement, Folic Acid), Choline Chloride, Minerals (Ferrous Sulfate, Zinc Oxide, Manganese Sulfate, Copper Sulfate, Manganous Oxide, Potassium Iodide, Cobalt Carbonate), DL-Methionine, Marigold Extract (source of Lutein), Rosemary Extract
Note things like beet pulp, corn meal, and by-products!
Here are the ingredients for Wellness CORE original:
Deboned Turkey, Deboned Chicken, Turkey Meal, Chicken Meal, Potatoes, Dried Ground Potato, Tomato Pomace, Natural Chicken Flavor, Canola Oil, Chicken Liver, Salmon Oil, Flaxseed, Carrots, Sweet Potatoes, Kale, Broccoli, Spinach, Parsley, Apples, Blueberries, Vitamins & Minerals, Chicory Root Extract, Yucca Schidigera Extract, Glucosamine Hydrochloride, Chondroitin Sulfate, Dried Lactobacillus plantarum, Enterococcus faecium, Lactobacillus casei, Lactobacillus acidophilus Fermentation Products, Rosemary Extract.
See how their ingredients include a variety of fruits and vegetables and meat, not by-products. Many people might think "meal" is a bad thing as in chicken meal, but all that means is the meat with water content removed. Kind of like oats vs oatmeal.
Both of those foods are dog foods, but the pattern is obviously similar, I'm just not as familiar with cat food. I know that they make a Wellness CORE for cats and that Natural Balance makes a Duck & Green Pea formula for cats which would be the cat equivalent of what we use.
I know many natural food stores have dog food samples, not sure about cat food, but its worth a try!