pymol - PyMOL is a powerful and comprehensive molecular visualization product for rendering and animating...
Avogadro - Avogadro is a free, fantastically easy to use molecule editor.
UCSF Chimera - UCSF Chimera is a highly extensible program for interactive visualization and analysis of molecular...
BKchem - BKChem is a free (as in free software :o) chemical drawing program.
Jmol - Jmol is a free, open source molecule viewer for students, educators, and researchers in chemistry...
VMD - Visual Molecular Dynamics - VMD - Visual Molecular Dynamics, molecular graphics software for MacOS X, Unix, and Windows