Not exactly free, however, this is a fine resource for viewing data and imagery... National Geographic DataDoors portal (www.natgeodatadoors.com), customers can select the exact area of coverage they want and order National Geographic’s TOPO! maps and i-cubed’s USA Nationwide Prime Imagery on CD-ROM or removable hard drives, or as a download. National Geographic Maps has scanned over 58,000 United States Geological Survey (USGS) quadrangles, color corrected them to create a consistent look and created a seamless map that spans all 50 U.S. states. The TOPO! map data is available at 1:24,000 scale in the continental United States and Hawaii, 1:63,360 scale in Alaska, and 1:100,000 scale in the continental United States. Digital Elevation Model (DEM) data is also available to help visualize vertical terrain and conduct spatial analysis and modeling. DataDoors delivers TOPO! maps and i-cubed imagery in many open formats, including TIF, JPEG, SID and ECW, and supports the selection of projection and data.