Geology
Texas National Resources Information System
The Texas Natural Resources Information System (TNRIS), a Division of the Texas Water Development Board, is the state's clearinghouse for maps, aerial photos, and digital natural resources data.
United States Geological Survey
The USGS serves the Nation by providing reliable scientific information to describe and understand the Earth; minimize loss of life and property from natural disasters; manage water, biological, energy, and mineral resources; and enhance and protect our quality of life. U.S.G.S. Mission Statement
National Archive of Geological Photographs
Searchable database of the British Geological Survey archives of geological photographs, over 100,000 images dedicated to the study of earth sciences.
Geology.com
Features satellite images, and many maps. Most useful feature are links to geological information by state. Maintained by faculty and students at the University of Pennsylvania.
National Geophysical Data Center
Geophysical data from the Sun to the Earth and Earth's sea floor and solid earth environment, including Earth observations from space.
Intute: Earth Sciences
This site has searches by subject headings in the earth sciences - geochemistry, structural geology and tectonics, geophysics, geomorphology, and geographical information systems. There is also a keyword e-journals search.