Blender - Blender is the open source, cross platform suite of tools for 3D creation.
TurboSquid - TurboSquid offers 3D models for professionals.
MakeHuman - MakeHuman is a free, open source, interactive modeling tool for creating custom 3D human characters.
STLFinder - The 3d models search engine.
Bforartists - Bforartists is a fork of Blender.
3DOcean - 3D Models & Accessories From $1 for 3D Models, Textures, Materials & Shaders, 2D Concepts...