I was in Red Sea this august and I took beautiful shots with my digital camera, a Canon Powershot G9. Today is very easy to become an underwater digital photographer, but you can also consider some techinical advice:
- front perspective are the best choice: don't take picture from above... they are to common! Sometimes you can have good picture from bottom...
- play with light: underwater, the sun have strange effects!
- take pictures also while doing snorkeling: you can have best color in this situation!
And here, a good tutorial
on underwater photography (EN)
(In this article some example shots from Red Sea Coral Reef)