Google\'s Sketchup is a nice, simple 3D-object modeler. Moreover Google has an enormous warehouse of 3D objects so that you actually don\'t have to do much modeling yourself if
It's probably not exactly what you're looking for, but I maintain a python library called pycollada. You could use it to export to Mathematica's format. I've also been working on an import/export/convert utility called meshtool which you could write a module for that would export to Mathematica's format.