RasMol
RasMol is a molecular visualization program for displaying and analysing molecular systems in 3-D. Details of the latest release (2.7.5) can be found on the pages RasMol or OpenRasMol (both seem to be the same page).
Jmol[edit]
On the Molecular Visualization Freeware page there seems to be a tendency to recommend the use of Jmol as a more modern alternative to using RasMol.