Flamingo nXt adds many features such as decals (a specific type of texture mapping), more advanced materials, large material libraries and also a plant generator.
AccuStudio - Lots of free objects, materials, plants and textures.
DOSCH DESIGN - Architecture, 3D models, scenes, textures and images.
These test commands are intended for internal development use, but may be helpful in some specific situations. They are not documented.