I spent ages looking at online sites to find the best deal a one way train ticket for 1 Adult and 2 children to Welshpool. Cheapest I could find was £50+ and that was if I bought a family railcard. Want down to my local train station and managed to get tickets for only £37 without needing to buy a railcard. Just thought this was worth mentioning - as all the online train sites say that they get you the cheapest deal!
Booking office staff in my local station are very, very helpful - will always find the best fare, even if it involves two tickets: if the ticket inspectors come round between station x and station y, use this one - if after station y, use this one'. (my blasted train 'operators' only allow off-peak between 9.30 and 4.30).