A wonderful site full of drawings of prototypical locomotives and freight cars that serve as the basis for all drawings found on this site. Also has sections full of prototype photos and other useful information related to trains.
A wonderful website focusing on roster shots of diesel locomotives for several railroads. Photos are accompanied by information such as manufacturer, order number, serial number, built date, history, etc.
(* Used as a source for locomotive serial numbers and histories)
Website focusing on roster shots of freight cars, passenger cars, and maintenance-of-way equipment for several railroads. Website includes detailed information including car builders, equipment data, dimensions / capacities, history, etc.