LOJIC Standard Data - Detailed maps and aerial photos of Louisville, Kentucky. - http://www.lojic.org/standard/viewer.htm
Aerial Photo Collection - Southeast Michigan, U.S., hosted by Wayne State University's College of Urban Labor and Metropolitan Affairs. - http://tools.comm.wayne.edu/media/low_res/aerial_photos/index.htm
NASA World Wind - Uses Landsat satellite imagery. - http://worldwind.arc.nasa.gov/
LandVoyage - Part free, part subscription service with in-house and United States Geological Survey imagery. - http://www.landvoyage.com/
GlobeXplorer - Includes aerial and satellite photographs, some high resolution. - http://www.globexplorer.com/