CGTrader - CGTrader is an online marketplace at which artists can sell and buy Revit and 3D models.
TurboSquid - TurboSquid offers 3D models for professionals.
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
SketchUp 3D Warehouse - The place to share and download SketchUp 3D models for architecture, design, construction, and fun.
Sketchucation - Sketchucation is a 3D SketchUp Community for students, professionals, designers, and hobbyists.
Free3d - Free3d (previously TF3DM)