Ikelite is the most popular manufacturer of camera housings designed to be used at significant depths. These are not designed for scuba-diving depths. There is really only one fish in the sea when it comes to cameras that are specifically designed for underwater use. The Nikon Nikonos system has been standard since Jacques Cousteau helped develop it in the early stages of his career. The cameras, rated to a depth of 165 feet, are still king.
Some lenses are designed for underwater use, some for land-only use and some are amphibious.
Because of the differences between the refractive properties of water and of air, lenses do not act the same underwater as they do on land. Avoid the all-electronic Nikonos IVa. The electronic Nikonos V is a terrific camera, but because of the danger of moisture on circuitry, is best purchased new. Priced to match. Whatever method you choose to shoot pictures underwater, it is of the utmost importance that you check every piece of equipment before you dive and that you thoroughly clean and inspect it after the dive.