US Geological Survey
Usgs: How to Build a Model Illustrating Sea Floor Spreading
This is a comprehensive website featuring how to build a model that illustrates sea-floor spreading and subduction. It has diagrams and pictures reviewing major geological concepts.
Institute of Marine Science
Forsea: If I Can't See It, How Do I Know It's There?
A diagram showing features of the seafloor and a laboratory experiment involving a model of the seafloor highlight this site. This is a good resource for teachers as well.
Extreme Science
Extreme Science: Challenger Deep
A short description of the world's deepest ocean trench. Includes diagram and map.