Getty Thesaurus of Geographic Names
Records for approximately 900,000 places provide vernacular, English, and historical names, as well as additional information about the places.
National Atlas of the United States
A "Best of the Web" winner! This USGS site provides an extraordinary interactive map of the U.S. Select from a variety of descriptive layers, including Biology, Geology, Transportation and Water. "This Atlas updates a large bound collection of paper maps that was published in 1970. Like its predecessor, this edition promotes greater national geographic awareness. It delivers easy to use, map-like views of America's natural and sociocultural landscapes."
USGS Mapping: Geographic Name Information System
"The Geographic Names Information System (GNIS), developed by the USGS in cooperation with the U.S. Board on Geographic Names (BGN), contains information about almost 2 million physical and cultural geographic features in the United States."