Yesterday we were killing time in Boulder and stumbled upon Art Source International on the web at http://www.rare-maps.com.
It's a relatively nice store, but even more amazing is their website which includes scans of all maps. If I owned a map/print store, this is exactly how it would work: Bricks and Mortar and online - both useful integrated stores.
Also, personally I'm interested in the series of George F. Cram maps of Denver which show the street maps as Denver formed including the streets around my house (supposedly built in 1894). It is currently on 3rd between Bannock and Cherokee, but it's clear that back then there was no such concept of streets in Denver and that manys treet names have changed.