Sculptris is a free digital sculpting/3D modeling program that is both powerful and extremely easy to use. It provides a digital modeling experience that is very similar to creating real life models out of clay, whereupon the virtual clay simply materializes from thin air and can be quickly shaped, prodded, cut, modified, and added. In practice the effect is very pleasant; allowing your 3D creations to grow organically, on-the-fly, as the idea(s) come to you.
Sculptris
Sculptris