A very nice bank of free high-quality themed 3D model bundles at 3D Render, which were specifically made available for the CG Society forum / 3DRender lighting challenges. It’s run by Pixar artist Jeremy Birn, and the current Challenge #23 is…
“a still life of a mad scientist’s table. […] deadline is July 30th, 2010. […] Use any 3d software and techniques you would like. Changes to the scene and models are allowed including adding new elements and changing existing ones. All 3D rendering techniques are allowed.”
When they say “adding new elements” I think they mean things like textures to buttons on the models, not adding complete new models? The downloads are open access. These are your base models (80k total) for challenge #23, currently freely available as OBJ and FBX among other file types…
And this is them in 3DXchange…
:: m y C L O N E :: 
Sorry, I was wrong about the $30 sign-up. You can post in the forums with a simple free sign-up, which means you can take part in the challenges.