(Note that all of the following has been brought within,
The National Map site.)
The
USGS (U.S. Geological Survey) have many US oriented maps, aerial images, and data sets available - and many are free. However most are at a regional level rather than a very local level.
Of particular historic interest is
TopoView, which facilitates access to maps in the USGS’s Historical Topographic Map Collection.
TopoView 2.1 is "a modern web application built on an open source mapping platform that is free of charge. The highly interactive service provides tools and procedures that allow users to easily find historic map scans from USGS’s Historical Topographic Map Collection and even compare those with modern day maps."