Tirediron made the good point - in order to give you a good advice it is important to know what you intend to do and what your budget is.
If you already have a camera and are not afraid to use your camera in an underwater case, get yourself a good one (Ikelite and Nauticam are brands that have a good reputation), but always consider that flodding is a posible accident. Usually a quality housing costs more than the camerabody that it is designed for.
In order to answer your initial question: I know some people using a Nikon D4s in a housing for undewater photography, while I, for occasional underwater photography, am using a Nikon S9100 in an Ikelite housing (good down to 40m/120ft), combined with two dedicated underwater lights with an 90 degree opening.