PyMOL is a powerful and comprehensive molecular visualization product
PyMOL is a powerful and comprehensive molecular visualization product for rendering and animating 3D molecular structures.
A chemistry tool that displays molecules and allows you to interact with them.
QuteMol- Interactive and Innovative Molecular Graphics
Is an open-source multi-platform molecular visualization program
Voreen allows interactive visualization of volumetric data sets.
Spartan Student is a serious molecular modeling package.