High resolution viewing images of almost all small and medium scale maps produced by the British Geological Survey (BGS) since mapping started in 1832. It includes the key 1:63 360/1:50 000 maps of England and Wales and of Scotland. All current BGS UK mapping & much more can also be accessed via Digimap.
The USGS (United States Geological Survey) store gives access to US and world geological and topographical maps and scientific reports.