CGTrader - CGTrader is an online marketplace at which artists can sell and buy Revit and 3D models.
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
TurboSquid - TurboSquid offers 3D models for professionals.
Free3d - Free3d (previously TF3DM)
Sketchucation - Sketchucation is a 3D SketchUp Community for students, professionals, designers, and hobbyists.