The American Memory Collection at the Library of Congress has some wonderful materials--particularly the United States railroad maps. These maps don't just list railroads, they often include numerous other political and geographic features as well. The dates of the maps range from 1828 to 1900. There are several ways to search the maps, but I find it most effective to browse by geographic location instead of doing keyword searches.
Always look over the entire page on any database or search site. There may be ways to browse the data in ways other than text-based searching.
The Railroad Collection at the American Memory Collection in the Library of Congress can be viewed beginning at this location: http://memory.loc.gov/ammem/gmdhtml/rrhtml/rrhome.html