SketchUp 3D Warehouse - The place to share and download SketchUp 3D models for architecture, design, construction, and fun.
Thingiverse - Thingiverse.com is the place to share digital designs for fabricating real, physical objects.
3DOcean - 3D Models & Accessories From $1 for 3D Models, Textures, Materials & Shaders, 2D Concepts...
3DExport - 3DExport is a 3D model marketplace where you can buy and sell 3D models, CG textures and digital objects for 3D printing with royalty free. Professional 3D models - 3DExport.com
Cults 3D - Cults is a marketplace that connects designers and people who want to 3D print some objects.
CGHero - Outsource 3D and CGI Production Platform