ChemAxon's MarvinSpace Viewing Applet
This MarvinSpace viewing applet is part of the Free Web package provided free for academic and non-commercial use by ChemAxon.com. By default, the viewer loads with King Cobra venom(!), but you can select to view any .mol or .pdb file you have on your local drive, or load a file from the RCSB pdb database.
Notice that the tool bar at the top of the viewing window can be "undocked" to float above the applet window so that you may view all of the tools available. The best way to learn how to use this tool is to play around with it. If you don't have any files to view on your own computer, try some from the RCSB.