Websites with 3D models for printing on a 3D printer
Thingiverse
https://www.thingiverse.com
MyMiniFactory
https://www.myminifactory.com
GrabCad by Stratasys
https://grabcad.com
YouMagine by Ultimaker
https://www.youmagine.com
Free 2D & 3D
https://www.tracepartsonline.net
TurboSquid
https://www.turbosquid.com/Search/3D-Models/free
TinkerCAD, ex Autodesk 123D Gallery
https://www.tinkercad.com/things/
Instructables
https://www.instructables.com/howto/3d+printing/
cgtrader
https://www.cgtrader.com
3D Warehouse by Google SketchUp
https://3dwarehouse.sketchup.com
yobi 3D
https://www.yobi3d.com
3D Content Central by SolidWorks
http://www.3dcontentcentral.com
Smithsonian Institute
http://3d.si.edu/
NASA printable models
https://nasa3d.arc.nasa.gov/models/printable
Pinshape
https://pinshape.com/
Youimagine
https://www.youmagine.com/
Cults3D
https://cults3d.com
Prusa Prints
https://www.prusaprinters.org/prints
3DToday
<< In search of inspiration >>
Shapeways
https://www.shapeways.com
Sculpteo
https://www.sculpteo.com/blog/
formlabs
https://formlabs.com/blog/
Materialise
http://www.materialise.com/en/blog
http://www.materialise.com/en/cases