Have you tried TurboSquid...their claim is for 250,000 3D objects in various formats....quality seems pretty good...guess it's all relative to what you need. Also, try Templates.com. Not necessarily cheap, but seem to willing to work with you for model versions in some cases.
For 3D models of the human body, try Zygote and their 3dscience.com website. Pricey, but kinda gruesome in detail. :)
oops, edited in the links:
http://turbosquid.com/?gclid=CIHVrKGY-KICFQ1HnQodlgq6fw
http://www.templates.com/product/3d-models/
http://www.3dscience.com/