Free 3D Models for 3D Printing

These are the websites with the major repositories for finding and downloading free 3D models for use with a 3D printer. The sites files range from very simple free 3D models to very complex 3D models.
3D Content Central
3D ContentCentral hosts free 2D and 3D CAD files from engineers and firms. You can also request models.
3dcontentcentral.com
3D Parts Database
The Shapeways 3D parts database is a place where you can download free 3D models free for 3D printing. The files currently in the database have all been tested and printed by Shapeways and all “print for sure.” Here are some fun materials you’re able to print with:

    1. Gold plated brass.
    2. Released for a limited time: Elasto Plastic that’s flexible and impact resistant. More information here.
    3. Clothing such as the gown worn by the Queen of Burlesque.
    4. Sterling silver cutlery so you can eat like they will in the future and silver pendants.
http://www.shapeways.com/
CG Trader
CG Trader has both chargeable and free models, both those ready for 3D printing and those not. You’ll have to use the filters to select just the free models.
http://www.cgtrader.com
GrabCAD
GrabCad is a site for engineers to show off and share their CAD works, with over 75,000 free models available. .stl filter available.
https://grabcad.com
TurboSquid
TurboSquid is a large repository of both pay-for and free 3D models. There’s no area dedicated specifically to 3D printing, but there are selectable filters such as .stl and .sldprt (Solidworks part).
http://www.turbosquid.com/
Thingiverse
Thingiverse is a huge community of people who create and share 3D designs freely, so that all can benefit from them. Widely used by the RepRap Project, and by 3D Printer and MakerBot operators.
http://www.thingiverse.com/
http://www.tracepartsonline.net
Trace Parts Online
TraceParts is a huge 3D parts database founded in 1989 with some very complex CAD files available in numerous formats, including .stl.
http://sketchup.google.com/3dwarehouse/
Trimble 3D Warehouse
The Trimble 3D Warehouse (formerly Google 3D Warehouse until purchased by Trimble) is a free, online repository where you can find, share, store, and collaborate on free 3D models created in SketchUp. This is a great place to look for models of famous buildings, as SketchUp interacts with Google Earth.