This is an area where you want to carefully weigh the features of each camera that meets your specific diving photography/video needs. Some cameras have features that you may not want in a dive camera, but desire in a land camera. So the first step is to decide if this new camera will be dedicated to diving or if it will be dual-purpose.
If it is going to be dual purpose, consider your megapixel needs if you are going digital. The mp level makes all the difference when it comes to editing your shots or taking video clips. Sure a 4mp like my Canon Powershot A80 might be fine for some applications, but it is old-technology by today`s standards.
Zoom and macro features are nice to have built-in, BUT some housings do not support external lenses/filters like those dedicated and designed by companies like Sea Life or Sea and Sea. External lenses/filters are another thing to consider for your specific needs. Sure, you may not think you need them now, but you might discover the more you use the unit the more you want/need lenses/filters.
Diver feed-back is important. See what divers have to say about the different units they have used, even if a unit was rented/borrowed for a short time. Of course, some divers are biased to one specific brand or model becuase it has been trust worthy for that specific diver (who might have only used the unit a handfull of times). www.scubaboard.com has a section dedicated to underwater photography and underwater video. Be sure to ask for some feedback there or simply read up.
I have had good luck with a couple of Sony models with housings, the SeaLife mini digital, the Canon Powershot series with housing, and a Sony video package with Ikelite housing. The only unit that gave me any grief was the SeaLife DC300 which worked wonderfully in the freshwater, but flooded the first time in saltwater.