Found this recently. Immense...
Ordnance Survey map data have been used to recreate the geography of Great Britain in Minecraft - the largest such map to use real-world information so far with over 22 billion blocks used.
You can get it from the Ordnance Survey website: http://www.ordnancesurvey.co.uk/inno...p-britain.html
It's a big file, though: 345MB compressed, 3.6GB uncompressed.