Links

Clubs / Associations

Australian Model railway Association (AMRA)
British Railway Modellers of Australia (BRMA)
Model Railway Electronics Group (MERG)
N Gauge Society (NGS)
N Gauge Forum (NGF)
Talking T Gauge Forum

Commercial software (all with free / demo versions that do something useful)

AnyRail Layout Design Software
PC-Rail Railway Simulations
SIAM Railway Simulations

Reference Books

Paul Mallery, Electrical Handbook for Model Railroads, Parts 1 & 2
    These two books are a complete survey of the whole field, mainly non-DCC.
    Includes a great deal that you won't find anywhere else (especially in part 2).  Highly recommended.

Roger Amos, Complete Book of Model Railway Electronics
   Some useful circuits here, though I wouldn't exactly call it "complete"..