DeleD CE - DeleD is a 3D modeler and level-editor combined into one.
Blender - Blender is the open source, cross platform suite of tools for 3D creation.
3D Ripper DX - With 3D Ripper DX you can:
Sculptris - Sculptris: Enter a world of digital art without barriers.
Sunny 3D - With ultimate simple user interface, you can create 3D model by using freehand sketch and directly...
ZBrush - ZBrush is a digital sculpting and painting software solution.