Geosciences title 
Geological Sciences:
USGS's view on Volcanoes - United States Geological Survey takes on volcanoes across the world. Includes methods on monitoring and studying volcancoes.
Volcanologist's Resources On-line - An excellent introduction to visual computer applications of the volcanoes and information, using models, photos, and animation. From Japan.
Introduction to Plate Tectonics - ABC's of plate tectonics, everything you always wondered or are curious about. This shows simplicity of how plate tectonics work and their wondrous source where it comes from.
EarthWaves - home of the environmental sources of earthquakes, ozone deletion, and more.
Earthquakes - Understanding how earthquakes work, this is an interactive computer program that shows how they work. From Cal State L.A. University.
Earth Sciences:
All about Earth - Understanding Earth more and following its cycle. 
GeoClio - Tells the history of geosciences & geology.
Extreme Science - Survey of scientists who are doing what kind of experiments in the natural world. Baddest of all, what are they? Find out here.
PlanetDiary - A look at the diary of what phenomena Earth is experiencing through. Includes measurements, data, and other tidbits to explore Earth.
Cloudy Skies *NEW* - A very neat and well layout web site devoted to clouds, weather, thunderstorms, and more. Check it out. Gorgeous pictures, too.