Like everything, there is an increasing amount of options when it comes to what to feed your cat. However, most of these can be grouped into a couple of basic categories, these are dry foods, and moist foods.
Dry cat foods can be served dry, or optionally moistened with water if you suspect your cat prefers it that way. Such dry foods contain moisture content of approximately 10%. A great benefit of dry foods is that it is possible to leave them in your cats bowl for extended periods of time - allowing your cat to peck away at the food as it desires. This is something that cannot be done with moist foods, which will lose their moisture over a period of a few hours.
Cat foods that are moist generally are found in cans, while dry foods are more commonly found in boxes. Moist foods have a good balance of fat, protein, and a majority of liquid moisture.
In addition to dry and moist foods, it is now possible to find an in-between - that is, semi-moist cat foods. These are often an excellent choice for more cats because they have an optimal balance of nutrition, and are available in a wide variety of tastes.
Be certain to feed your cat a variety of foods, and be sure the food is at about room temperature. If you feed is the same thing all the time, it may become closed minded to other possible foods, which may be a problem if the primary source is no longer available. Cats, like humans, can become addicted if they are not kept open minded.
Allosia Online Books [http://www.allosia.org] has a section of online cat books [http://www.allosia.org/books/cats-1.html].