Free 3D testing models.

[Ryzon]

There is a site called Turbo Squid. It has tons of models both paid for and free. Due to many scammers out there and digital thieves I would not purchase and models from there but would use the free ones as placeholders till you have your own made or purchased from a more viable source. Below is the link to the site just adjust the search filters to show only free models.

http://www.turbosquid.com/Search/?max_price=0&keyword=free&min_price=0

[SolarPortal]

just came across a website of 60 free model sites:
http://www.hongkiat.com/blog/60-excellent-free-3d-model-websites/

you might be able to get some test meshes from any of those sites.

[vachyre]

The Smithsonian Museum has acknowledged that it contains for more great treasures than it could ever exhibit in a lifetime and so has begun scanning all of their collection in 3D. These models are free to download from their site and come in a variety of accessible formats

http://3d.si.edu/