"Here's a list of ingredients to AVOID -
Corn - It's undigestable! This is used as a cheap filler for almost all dog and cat foods! This has almost no nutritional value, and passes straight through your pet, coming out as additional waste. Ontop of that, it's a very common allergen in dogs and cats!
By-Product- Some by-products are worse than others, but all by-products are an inconsistant source of meat protein. You never really know what's in by-product meal, but it can range from diseased livestock, horse remains, roadkill (!), euthanised animals from local shelters (!!!) and 4-d meats (all seen in meat by-product meal) to unfiltered intestinal tracts, feathers, brains, feet and waste (poultry by-product meal). Some say that by-products aren't all bad. Why? Well because an animal would eat all that in the wild, right?! Nope, not necessarily. By-products can contain high traces of chemicals used in euthanasia, as well as meat rendered but still tainted with poisons and deadly bacteria. In the wild, most animals would never encounter these things, and would probably die if they did. The 'filler' that the animals would gain in the wild from eating other animals can be replaced with much, MUCH cleaner, healthier, and safer ingredients (seen in the second list).
Peanut Hulls, Mill Run - This is essentially what they sweep off the floor from the processing plants. It's litereally the hulls of peanuts, scraps from trees (including bark), and whatever else employees happend to drop on the floor that day. Science Diet will tell you it's fibre! Unfortunetly, we really don't have the slightest idea what's in the 'mill run' that day.
And here's a list of ingredients look for -
Whole meats or deboned meats (i.e Chicken, Turkey, Bison, Venison) - You're getting exactly what it says you're getting. Whole meats, usually quality cuts of whatever is listed. This is meat alone, contains no internal organs, no mystery chemicals. Genereally the best quality meat you can get in pet food.
Fruits and Vegetables - Such as fresh blueberries (a natural antitoxidant!), fresh apples (yummy, and healthy!), sweet potatoes (reliable source of fibre, though doesn't agree with all dog's tummies). Again, you're getting what it says, these are fruits and vegetables ground up in the food. This is the source of fibre and plant material that a dog or cat would normally be getting from eating the stomach of prey in the wild. It's carefully balanced in premium foods, and is generally not a main ingredient.
Cat food: Meat vs. oh god
Cats are carnivores. In the wild, they live purely off of meat, and off of the stomach contents of their prey. In your home, they also need a predominantly meat-filled diet, though some amount of roughage and fruit/vegetable content help to maintain healthy digestive and urinary tracts. Cats do not need added carbohydrates.
High carbohydrate content makes cats fat, plan and simple. And corn is hard to digest. High-quality foods contain no corn, and little grain. Vegetable matter is fine, just not grain.
Nature's Variety Prairie
Evanger's (makes only wet) (NOT the vegetarian formula, duh.)
These all come with a pretty hefty pricetag.
For the rare cat who's allergic to poultry, California Natural and Prairie are two of the few brands of cat food that offer poultry-free formulas. (Prairie used to offer the only beef-based dry cat food I've ever seen, but it appears to have been discontinued.)
Be careful with Innova EVO. Though it's an ultra premium food, it has a very high protein content and cats prone to kidney issues shouldn't eat it. For a healthy cat, however, it's one of the best foods on the market. I recently switched my cats to EVO from Chicken Soup (see below), and they absolutely love it. Some people report more aromatic stools, and for the first few weeks I noticed more stink around the litterbox, but now that they've adjusted the odor's decreased.
I say "Wysong?" because Wysong's website creeps me out. It seems like it's trying so hard - something's GOT to be wrong here. Either they're all dirty hippies, or they're aliens, or... something. Regardless, Wysong makes prescription diet formulas that have Hill's beat.
And Evanger's is just crazy. One variety is called "Whole Mackeral with Gravy." It is, in fact, an entire mackeral cooked in a gravy to make it nutritionally-complete for cats. It's even grain-free. Other varieties are chock full of organic ingredients. And it costs less than Prairie's canned food.
Solid Gold has impressive wet and dry food. Solid Gold wet is similar in cost to Evangers, and has the consistency, odor, and appearance as regular canned tuna. (One of my cats dislikes pate-style wet food, and Solid Gold is her favorite wet.)
Taste Of The Wild
Pet Promise (wet)
Newman's Own Organics
Premium cat foods contain no by-products.
At the moment, Merrick's website doesn't list any dry cat food formulas. Merrick's wet cat food formulas seem pretty good, but they contain carrageenan - a binding agent to give the food "better consistency." Carrageenan isn't "unhealthy," but I used to work in the deli business, and let me tell you, carrageenan does some pretty nasty stuff with meat.
A couple other "premium" brands also contain carrageenan, so I don't buy them, but they're still nutritionally good.
Blue Buffalo is available at PetSmart, and at Petco. Pet Promise's slogan is "Let By-Products be Bygones;" and Blue Buffalo has "nutrient clusters" (or whatever they call them), meaning the vitamins and minerals are cold-formed and not cooked with the meat, so they don't lose potency.
I used to feed my own cats Chicken Soup, and I'd still recommend it as a food. I used to get it for about the same price as Iams. I free-fed the dry formula, and both my cats maintained a healthy weight. My cats didn't care as much for its wet formula, though. Though they loved the dry!! (Go figure!) But, now I can't find it in my area. It was a big disappointment when they stopped stocking it.
Wellness has a good ingredient list, and is one of the higher rated premium brands. My cats seem to like it OK.
Nutro (Complete Care and Max Cat)
Pet Promise (dry)
These formulas are sort of "in-between." They're not bad, and I wouldn't immediately try to convince someone to switch from these... but there's much better stuff on the market. Nutro and Eagle Pack contain some corn, and Diamond Naturals contains "chicken flavoring." (If it was so natural, wouldn't it already taste like chicken? Or does chicken taste like anything?)
Also, rumor has it Nutro will be changing its formula soon, and not in a good way - so if you feed Nutro, keep watch over your bag's ingredients.
Royal Canin also contains corn, and I don't buy its claims that "scientific studies" show how individual cat breeds require "dramatically different diets to address significantly different nutritional requirements." I see Royal Canin as the biggest practitioner of marketing BS among all "quality" pet food manufacturers.
Wysong dry cat food contains corn, which is odd since Wysong's ingredient list is otherwise excellent.
Purina One/ Purina Cat Chows
I don't like how Science Diet's main ingredient is corn, but let's face it - there's much worse crap out there than Science Diet.
Iams and Eukaneuba are practically the same, and Purina One isn't much different.
And I'm downgrading Trader Joe's to "acceptable," now that I've someplace with a Trader Joe's and have seen the food first-hand. Some Trader Joe's formulas may be better than the "acceptable" category, but recipes vary and some are better than others. Recently, I went with a friend to Trader Joe's because she wants to start feeding better food to her cats. We looked at 4 varieties of wet, and 3 contained un-named "meat" ingredients; the dry contained corn. So if you feed Trader Joe's, be sure to read the ingredient labels fully.
Whole Paws has an impressive ingredient list and excellent consistency, and I once picked up a whole ton of it at Big Lots. However, most of my cats still loved it and there was no indication of health-related issues, but domestically-manufactured foods from smaller companies seem safer these days.
Many of these foods contain a significant amount of by-products as protein source, but they're still healthier than...
Special Kitty, or whatever Wal-Mart calls its house brand
Other Generic Store Brands
Basically, anything containing corn and by-products as the primary ingredients will damage your cat's health. Cheap foods cause poorer, less glossy coats with more matting and shedding, as well as more frequent and more aromatic defecation. Also, much as there's currently a human obesity epidemic, there seems to be a feline obesity epidemic - cats are indoors more and are less active, so they're getting fatter and are developing diabetes and other disorders at younger ages.