ERA - Electric Railroaders' Association, Inc.
Penn Pilot - Historical Aerial Photo Library, Pennsylvania Geological Survey, Penn State Center for Environmental Informatics
Pennsylvania Trolley Museum
Pittsburgh Railways OnLine
Steamboat Building in Elizabeth, PA - Historical Photographs of Charleroi, Monessen, Belle Vernon, and Donora, and Lock #4 with an emphasis on rivers, bridges, and locks.
Stuff That's Gone - Historical photographs, and photos and videos of artifacts from railroads, highways, coke ovens, and trolleys in Pennsylvania including West Penn Railways in Brownsville, Dunbar, Allison, Jeannette and other towns in Pennsylvania.