I use trains quite often and apart from the official National Rail site: have found these alternative site useful.

Accessible train times
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
Help with our ridiculously complicated ticket prices

Open Train Times
Here’s a signalling plan for Crewe:

Raildar – historic train times
Useful when making a complaint and asking for a refund!

Real Time Trains
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:

Performance and reliability
Live and historical information.

Show times of steam trains running on the mainline.

Trains Can Be Cheaper
Site to help you get cheaper tickets

Information about trains stations and lots of diagrams.