A commonly used program for visualizing molecules. It can be used with a range of file formats and the display can be choosen (e.g. wireframe, ball-and-stick, space filling, etc.). The original version was written by Roger Sayle of Glaxo around 1990. It is freely available.
www.umass.edu/microbio/rasmol/getras.htm A downloadable version of RasMol from the website of the University of Massachusetts Amherst