Realtime Trains (RTT), Open Train Times (OTT) and National Rail Enquiries (NRE) are all invaluable for cross-checking details and for any last-minute changes.
Realtime Trains is very useful for checking recent past history for comparing actual routes against booked routes, for example did a booked train really use a specific platform.
Actual routes taken (path, platform and line details) are shown as emboldened text after the event, but there are odd instances where this is not 100% reliable.
OpenTrainTimes has a useful search facility – see details on the About page - which can be found at http://www.opentraintimes.com/schedules.
Discussion on travel over unusual track – including weekly postings on route diversions (WEEKEND) - can be found on Gensheet, and anyone who does not already subscribe to this Yahoo group is encouraged to do so.
The Branch Line Society (BLS) promotes travel over unusual routes – amongst a general interest in the study of railway infrastructure and history of networks – and should also be accorded serious attention.
Excellent information on regular booked services over unusual routes (primarily at the ‘Baker’ level) is provided by the Passenger Train Services Over Unusual Lines (PSUL) website.
Any railtours that are known to be booked over unusual routes (again, primarily at the ‘Baker’ level) are usually listed on Railtours Advertising Rare Routes.
Railway Codes and other data includes track layouts for UK light rail, TIPLOC codes, and much more.
Finally, a useful publication is Baywatch published by the Kentrail Enthusiasts Group – contact scubatrack[at]yahoo.com for details.