Cardstock models are ideal for quickly populating a new layout or module, or building low relief buildings for background and backdrop applications.
Illinois Historic Preservation Society – has over a dozen free historic buildings that may be printed and assembled. A must see resource.
The following are commercial, paid products, but all offer some free downloads.
ScaleScenes - “download and print realistic model railway kits from your PC now!”
CleverModels – “craftsman card models and high resolution texture sheets”
PaperCreek – sells laser cut paper craftsman kits for structures and textures.
ModelBuilder – “”Use our building software to inexpensively add hundreds of paper buildings to your layout. Print realistic buildings or backdrops for your model train layout.” USD: $45, OS: WinXP.