NOAA
Noaa: Ngdc: Images, Visualizing Data
The National Geophysical Data Center has transformed extensive ocean research into colorful video, 3D maps, charts posters and more! This site starts off with a film clip of a dive into the Marianas trench and then lead you to other...
Extreme Science
Extreme Science: Challenger Deep
A short description of the world's deepest ocean trench. Includes diagram and map.
Other
Ocean Trenches
A rather detailed explanation of how trenches form and why. No graphics, but some interesting explanations as well as links to other sites and extensive reference list.
Woods Hole Oceanographic Institution
Woods Hole Oceanographic Institute: What Are the Deepest Parts of the Ocean?
A brief description of the ocean's deepest parts.