Flamingo nXt adds many features to the native renderer such as decals (a specific type of texture mapping), more advanced materials, large material libraries and also a plant generator.
Accustudio - Worldwide AccuRender/Flamingo resources supporting AutoCAD, Revit and Rhino. Lots of free objects, materials, plants and textures.
These test commands are intended for internal development use, but may be helpful in some specific situations. They are not documented.