As a federal depository library, the Map and Geospatial Hub maintains a collection of topographic maps produced by U.S Geological Survey (USGS). Topographic map scales include 1:24,000, 1:52,500, 1:100,000, 1:250,000 and other scales for historic maps.
Since USGS no longer distributes print topographic maps, see National Geologic Map Database and the USGS Store link below for information on downloading maps.
Download USGS topographic maps or order paper copies.
Booklet from the USGS on interpreting symbols on topographic maps.
Libre Map Project
The Libre Map Project houses map image files (TIFF), GIS Data and documentation. Its data includes 24k scale USGS DRG data, SVG boundary files, TIGER/Line data and GeoNames. Users can search by state, place name, and feature, and data is available in tiff, tfw, fgd, and TIGER/Line formats.
Microsoft Research Maps (formerly known as: TerraServer-USA)
TerraServer (by Microsoft) provides free access to both USGS topographic maps and aerial photographs.
Perry-Castañeda Library Map Collection - Topographic Maps
The University of Texas Libraries scanned print maps and made them available on the web.