Geology of Britain [British Geological Survey] - online interactive webpages which allow you to investigate the geology of Britain including; bedrock; superficial deposits; TM Landsat imagery; fossil localities.
Office of Coast Survey - Historical map and chart collection including images from the U.S. government’s historical surveying and mapping. This collection contains scanned images including nautical charts, bathymetric maps, and city plans. Electronic copies are available through a free download to the public.
Old Maps Online - a portal to locate historical maps in libraries around the world
OneGeology - international initiative creating a dynamic digital geological map of the world. The first prototype of the OneGeology Portal is available to view.
Topographic U.S. Maps - The U.S. Geological Survey (USGS) National Geospatial Program is converting historical printed topographic quadrangles to an electronic format. Maps can be downloaded for free even though it appears that you have to pay money, you only have to pay for print copies of the maps.