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...
TurboSquid - TurboSquid offers 3D models for professionals.
Sketchucation - Sketchucation is a 3D SketchUp Community for students, professionals, designers, and hobbyists.
SketchUp 3D Warehouse - The place to share and download SketchUp 3D models for architecture, design, construction, and fun.
Free3d - Free3d (previously TF3DM)