I use trains quite often and apart from the official National Rail site: www.nationalrail.co.uk/times_fares/ldb.aspx have found these alternative site useful.
Accessible train times
https://traintimes.org.uk
Great for planning journeys. Gives advice on ticket splitting and you can export useful timetables (which will show you other trains if you miss your connection).
BR Fares
http://www.brfares.com
Help with our ridiculously complicated ticket prices
Open Train Times
www.opentraintimes.com
Here’s a signalling plan for Crewe:
https://www.opentraintimes.com/maps/signalling/crewe#T_CREWE
Raildar – historic train times
http://raildar.co.uk
Useful when making a complaint and asking for a refund!
Real Time Trains
www.realtimetrains.co.uk
One of my favourite sites! Shows where your train really is and the times for places between stations. I keep alternating between the simple and the detailed sites:
www.realtimetrains.co.uk/search/detailed
Performance and reliability
http://trains.im/ppm
Live and historical information.
Steam
http://www.uksteam.info/index.htm
Show times of steam trains running on the mainline.
Trains Can Be Cheaper
https://www.trainscanbecheaper.info
Site to help you get cheaper tickets
Traksy
https://traksy.uk/live
Information about trains stations and lots of diagrams.