Maps

National Atlas: The web-only National Atlas from the U.S. Geological Service coordinates gerographically oriented data from more than 20 federal agencies. Use MapMaker, an interactive tool with thematic data layers, to create custom maps of any area in the U.S. at any scale.
Perry-Castañeda Library Map Collection: Housed at the University of Texas at Austin, the Map Collection holds more than 230,000 maps covering every area of the world, making it perhaps the most exhaustive map collection on the Internet.
National Geographic MapMachine: Find nearly any place on Earth, and view it by population, climate, and much more. Plus, browse antique maps, find country facts, or plan your next outdoor adventure with our trail maps.
Map History/History of Cartography THE Gateway to the Subject: Use this site to find worthwhile information about old maps, both on the web and in the real world. The site's 100 'pages' offer comment and guidance, and over 3,000 annotated links - selected for relevance and quality.
geodata.gov: U.S. Maps & Data: Use this site to create maps with data elements from categories including agriculture, biology, boundaries, ecology, economics, geophysics, health, transportation, and water resources.