I found 7 sites that have really awesome and 100% free 3D models. Make sure to only search for .obj, .3ds or Cinema files since some models only come in Maya or Max formats. Also make sure to check the copyright info to make sure you’re good to go on all of these.
1. Turbo Squid
This is the premiere place to find 3D models. They have a huge paid section, but if you simply type “free” into the search, it will come up with hundreds of awesome free models. www.turbosquid.com
2. Exchange 3D
This has quite the collection, with a little bit of everything from cars and trees to furniture and interior models. http://www.exchange3d.com
A great resource with tons of characters and cars. http://thefree3dmodels.com
4. DMI 3D
This site has amazing vehicles, anything from WWII tanks to modern race cars. A lot of them come in .lwo format which is Lightwave, but they open great in C4D. http://www.dmi-3d.net/
A little resource but a nice range of high quality models. http://www.oyonale.com
A little bit spammy, but if you can get to the models they looks great. They have cars, furniture and technology among others. http://www.3delicious.net/
This is pretty funny, NASA actually has a model library of everything space, from models of astronauts to lunar modules to shuttles. Some aren’t the most detailed, but if you need some space objects, this is a great place to check out. http://www.nasa.gov
If you guys have any other free 3D model resources you recommend, please put them in the comments, I would love to know about them. Thanks!