There are very few cameras that are rated for underwater (without a special housing).
And these are only rated for shallow dives (less than 10 feet deep).

If you want to dive deeper, you have to use a special housing.

You might look at the newly announced Olympus Stylus 720SW.

Here is their press release:

http://www.dpreview.com/news/0601/06012602olympus_720sw.asp

...
..
.