Digitized collection (3,000+) of historic and contemporary maps. Many maps are U.S. government originals and may be downloaded and used without copyright restrictions. Also has links to websites for maps worldwide. Main map arrangement is by continent, further broken down into regional and city maps, among other categories.
Primarily for data on hydrologic regions (HUC), but also has data for most features. Using a map, locate geographical features and find coordinates, hydrologic data on the feature (and USGS topo map info).