Understanding Earth - Course Textbook
USGS - United States Geological Survey
GSC - Geological Survey of Canada
MGS - Minnesota Geological Survey
NASA - National Aeronautics and Space Administration (yes, they do geology too!)
JPL - Jet Propulsion Lab at Caltech
Geologic Time Scale - UC Berkeley
Plate Tectonics - USGS site
Stephan Reynolds - a very cool site with great tutorials, graphics, and links
Recent Earthquakes - USGS site
Recent Earthquakes - IRIS site with great education links