Ask a Geologist -- US Geological Survey geologists answer questions posted to them via the internet.
An Overview of Production of Specific U.S. Gemstones -- The U.S. Geological Survey has made this publication available online. The great photographs are courtesy of the Smithsonian Institute.
The Mineralogy Database -- Lots of information, some amazing photographs, and all provided in six different languages.
A Gem of a Story -- "A live, interactive, televised electronic field trip for grades 7-12." This virtual tour takes you to through the Janet Annenberg Hooker Hall of Geology, Gems, and Minerals at the Smithsonian National Museum of Natural History in Washington, D.C.