There are 11 forums I go to every day, in fact many times a day.
Rails of the World, my forum and naturally my home forum.
Trackside Modeler, small, not much traffic.
Trains.com - General Discussion.
Trains.com - Layouts and layout building.
Western Rails.
The Layout Party, small, little traffic.
2Guyzand sometrains, fair traffic, good people.
Model Train Forums - Fair traffic.
TrainBoard.com - Fair traffic.
The Gauge.
ModelRailroadForums.com.
I also make the rounds of some other railroad forums, but there's not much to them. The only other forums I go to are some computer forums (one of my hobbies is building and programming computers), they're all invitation only, so I can't put their names here.