There are a couple of other indoor scales you may come across as you explore the world of model railroading, like O, OO, TT and Z-scale.
For more information about these scales, refer to the "Basic Model Railroading" book by Kalmbach, available here in the WP&YR trainshoppe.
Also you might find these websites interesting:
http://www.micro-trains.com (Z-scale trains)
http://www.hornby.com (OO-scale trains)
http://www.ttscale.com (TT-scale trains)
http://www.pecosriverbrass.com (O-scale trains