When it comers to cat food there is a clear winner, and you can't buy it at the supermarket. Most major cat foods are stuffed with fillers and dyes that are, if not downright harmful, detrimental to their long term health. Raw foods like
Nature's Variety Instinct Raw line or
New Zealand's Country Pet Naturals are both excellent choices.
If you decide to go with these foods you can expect the quality of your cat's coat to improve dramatically, that they will litter box less often and they the litter won't smell nearly as bad as it did when the cat ate kibble.
Where do you get these brands as I have never heard of them? My kitty is soooo fussy, I can't even get her to eat raw meat most of the time. I like to feed her as much healthy food as possible so I'm always willing to try new brands. As you have mentioned, you never really know what is in the cheaper brands of food.