Administrative boundaries for historical political entities?

Question

Similar to Seeking administrative boundaries for various countries?, do you have any data sources for historical political entities, and their administrative sub-units?

Data from any continent, any period in time works.

Edit: Some examples of shapefiles I would like to have:

• Kingdom of France and its duchies & counties: example.
• The British Isles: example.
• List of states under the Holy Roman Empire: example.

Answer 1

National GIS Resources

NHGIS has historical data for the United States
Great Britain Historical Geographical Information System (GBHGIS)
The Great Britain Historical GIS (Main)
GBHGIS Data Access
National Heritage List for England (NHLE) Listing Data
The US National Historical GIS
The China Historical GIS
Chinese Civilization in Time and Space
Taiwan History and Culture in Time and Space
The Belgian Historical GIS
The Historical GIS for the Netherlands
Historical GIS Germany
Russian Historical GIS
Japan Historical GIS
China Historical GIS

More Resources

The Digital Atlas of Roman and Medieval Civilizations (DARMC)
Historical GIS Data resources listing via David Rumsey Map Center
Historical GIS Research Network
HistoricalGIS.org via Wayback Machine
Pleiades - Digital Ancient World Historical Atlas ORBIS: The Stanford Geospatial Network Model of the Roman World
CShapes - historical maps of state boundaries and capitals in the post-World War II period
European GIS-data-infrastructure on historical national and regional administrative boundaries and historical place names
Historical World Atlas Repository has global data starting from 2000 BC.