Because underwater photography is a specialized art, relatively few photographers attempt it. But it offers many exciting and rare photographic opportunities for fresh and truly different vivid images. Most often, photographers use a traditional film or digital camera covered in a watertight casing. Professionals prefer to use special underwater cameras.
Victor Amor
J.Lambusphoto
Scott (lundysd)
Numera Tokyo
National Geographics
Kenvin Pinardy
Sugarock99
Dustin Humphrey
source: http://www.smashingmagazine.com/2008/10/19/25-beautiful-examples-of-underwater-photography/