http://gopro.com/
http://www.contour.com/
These seems to be the in thing for any outdoor extremist. For what they do, the price is quite reasonable.
No preview screen, but both have goggle mounts (which would work well for underwater I would think) as well as sticky mounts for helmets if you ever go snowboarding.
GoPro is waterproof as is. The contour needs a special case, but the cool thing about that one is the built-in GPS function.
Both are available at a lot of electronics and camera stores I believe.
Edit: Whoops these are video cameras actually, but still pretty nice!