Most Libraries have map collections of one sort or another. Some, such as the Library of Congress (LOC), have digitized such a vast number that it seems as though you could never browse through them all. The LOC is also so big as to be unwieldy at times, and they archive their images in an assortment of formats which are sometimes cumbersome to download and convert in to a more easily readable form.
Smaller collections such as Michigan State University's are often more focussed, and when you are lucky they even offer good sized images. I say "smaller" when in fact, to quote their website:
"The Map Library houses a collection of general and thematic maps and atlases for every area of the world. The collection consists of approximately 212,000 sheet maps, 14,000 folded geologic maps, and 4,000 atlases, gazetteers and other reference aids including wall maps, globes, CDs and Internet-accessible resources. The collection is especially strong in Michigan, United States, Canada, Africa, Asia, and Latin America, though all areas are collected at some level. Specialized collections include 19th-21st century Michigan county atlases and plat books; a small Braille map and atlas collection of U.S. states and ...