This investigation will help you to:
When the Earth Moves: Seafloor Spreading and Plate Tectonics, National Academy of Sciences
Historical account of plate tectonic theory
This Dynamic Earth: The Story of Plate Tectonics, USGS
An account of the development of plate tectonic theory.
Plate Tectonics, USGS Earthquake Hazards Program
Lists links to many other educational sites about plate tectonics.