RailRailNational Rail 
"The gateway to Britain's national rail network." Includes live departure boards for many UK stations. An interesting idea, although still an experimental system - "some of the information shown may be wrong"!
The TrainLine.com
TheTrainLine provides impartial information on train times and tickets on mainland UK routes. It is as accurate and up-to-date as possible, and uses current timetable and fares information. TheTrainLine enables you to make your own travel plans and ticket choices, using a simple step-by-step electronic form. Secure online booking and payment is then offered.
UK Railways on the Net
Information and timetable links
Eurostar
Eurostar is the high speed passenger train linking London, Paris and Brussels. Eurostar can be booked online but requires registration. European rail companies have yet to offer online booking for UK residents but sites such as European Rail and Eurorail are useful for timetables and fares.