i use a (relatively) cheap nikon 4300 for mine, and i purchased a wide angle/macro lens for it. the only downside is that it can't focus beyond about 3 inches with the macro lens, so to get shots of zoos i nee dto plan ahead and move them right next to the glass and then wait for them to open back up again.
some of the newer high end cameras that take fancy lenses allow you to do macro deeper in the tank... a friend has a nikon d70 and a 300mm lens, and can take macro shots of things that are like 4 or 5 feet back in the tank... but that outfit would run over 2 grand to purchase
