PyMOL is a molecular graphics system with an embedded Python interpreter
designed for real-time visualization and rapid generation of
high-quality molecular graphics images and animations. It is fully extensible
and available free to everyone via the "Python" license.
PyMOL can be used to create images and animations with unprecedented ease.
It can also perform many other valuable tasks (such as editing PDB files)
to assist you in your research.

WWW: http://pymol.sourceforge.net/