One of the best investments I made as far as camera gear goes has been the Olympus Sytlus 790sw. While the camera only has  a depth of about three meters deep, it is more than sufficient to get decent pics of a variety of tropical fish in the waters of Thailand and islands like Koh Phi Phi.

Note:  I am way to chicken to dare try to seal my DSLR properly to take even better underwater pics . Since I am rather clumsy, and probably more lax than I should be when checking things like seals and gaskets, I decided I would rather risk losing a camera worth about $250 USD than losing the amount of money I have invested in my DSLR.