Get a couple dozen dives in before you get the camera Diving needs to be 100% automatic. Cameras require a lot of mental effort to use underwater.
When selecting a camera you should plan ahead. Do you want external strobes? If you do then plan out which ones and how they will be conected now, then buy the camera.
Why stobes? It's an imag quality thing. (Post another question asking about strobe if you want.)
All that said. I have a Canon A80. The 70 or 90 would be good too. depends on budget.
One thing to look at is batery life. The "A" series camera have four AA cells which gives
them good life. You do NOT want to be opening up the housing between each dive.
My A80 will do well over 200 shoots before the case needs to be opened. I have a 512MB memory card inside.
Learn to use the camera with your eyes closed on land, seriously you need to know the camera well _before_ you take it underwater. You can't read the little menu icons and the housing hides the writing on the buttons. Also learn how to use a good image editing software. No one's UW pictures look good right out of the camera. I use "gimp" see
www.gimp.org expect itto take a few weeks to learn any of the software.
BUt shop for a flash if you want one first. You may find that the flash you like supports only the Olyimpus or Nikon. AN A80 andhousing can be found for abut $400 total if you look around.
