Not sure if anyone is aware of this site (or if its even been posted here before) but its a massive collection of maps, and if you create an account (free) you can download very high-res images of all of them.

David Rumsey collection

i've found some really detailed images here that are simply a joy to pour over. hope someone else finds the site interesting

note: you'll need this part of the site to brose images

there's also a google earth viewer in which you can browse the maps in 3d.

great stuff!