Useful railway history web links evaluated and selected by a network of subject specialists are listed below:

Beyer Peacock
Beyer Peacock and Company built locomotives between 1854 and 1966. Information about the company and its locomotive

Gresley on line
Information about Sir Nigel Gresley, his locomotives, and the societies which continue his legacy

National Railway Museum
Home to the UK's national rail collection. Includes online exhibitions of collections, special events and information for visitors to the museum

Railway-studies Mailing List
From the JISCmail web

Steam Index: British steam locomotive history
Information on authorship of railway literature, biographies of mechanical engineers and locomotive types

Stephenson Locomotive Society
UK society for the study of railways and railway locomotion

UK Heritage Railways
A guide to the heritage railway scene in the UK and Ireland, including details of special events, trains and operating days for all steam railways