The camera I bought was a Canon® PowerShot A60. It's a 2 megapixel camera (1600x1200 maximum image size), which is modest by today's standards, but it seemed reasonable to go with a lower-end camera when I have no experience in underwater photography, and don't know how things are going to turn out.
As it happened, that camera turned out to be an excellent choice. Canon makes an underwater housing for it (see below), good to 130ft, and it worked fine. I made sure to clean the o-ring every night, and had no problems with leaks. Of course, the camera's built-in flash is somewhat limiting, but it worked quite well for macro shots.