The National Library of Scotland has a great online collection of old maps as well: http://maps.nls.uk/ http://maps.nls.uk/ - going back to 1500, with slippy ma

The National Library of Scotland has a great online collection of old maps as well: http://maps.nls.uk/ http://maps.nls.uk/ - going back to 1500, with slippy maps, side by side views, all sorts. It's not just Scotland, but the whole of the UK. A lot of them are georeferenced so you can easily flip through time and see how your local area changed. Licensing isn't as simple as USGS's though.