Here are links to Sanborn Fire Insurance maps that I have found. I can’t imagine a better resource for the historian or the modelrailroader researching a prototype for their layout:
The city of Rutland, Vermont > Maps:
http://rutland.govoffice.com/index.asp
Frankfort, Kentucky:
Alabama:
http://alabamamaps.ua.edu/historicalmaps/FireInsurance/1_County%20Index.html
Utah:
South Carolina: