Am Baile - Highland history and culture, including archive material from the Society
British Library Newspaper collection - copies of all newspapers. Held at Collindale, north London
Colour Rail - a large archive of colour photographs, with many from the 1950s and 1960s.
National Archives of Scotland, Edinburgh. Holds Highland Railway Company records, drawings, etc.
National Museum of Scotland, Edinburgh
National Railway Museum, York
The National Archives at Kew, London.
Ordnance Survey Maps, first edition
Scottish Architects - biographical details. Includes several who worked for railway companies.
Scottish Archive Network, details of historical records in 52 public archives in Scotland
Scottish Map Library, part of the National Library of Scotland
Tracking Railways Archive Project, listing railway related archives throughout the country.