For those of you interested in old topographic maps, Novacell Technologies, at http://www.novacell.com, has historic topos for the entire United States. Maps are available from the 1880s to the 1970s.
That could be a nice resource. I have used topo maps for well over 30 years for every thing from hunting to backpacking. Now I find them useful for MDing, especially finding old sites.
I have bought a few old topos on eBay but the shipping drives up the price 50%.