I am sure Sugarcatmom will be here to give some excellent advice soon.
First thing: NO DRY FOOD.
Cats should be eating canned food to flush out their kidneys and bladder as they have a very low thirst drive.
Second: Species appropriate food to ensure the urine ph is kept at an acceptable level which is 6-6.5. Cats are carnivores and should be eating meat, not grain or potatoes.
Raw would be the absolute best food, then my personal favourite, Natures Variety Instinct or Wellness, grain free flavours.
http://www.catinfo.org/
http://www.peteducation.com/article....+1402&aid=2729
Some info on cat nutrition. After reading this, you will be wondering why vets are not pushing raw diets as some of cats essential nutrients come from RAW meat, not cooked.:
http://maxshouse.com/feline_nutrition.htm