ChemDraw (now ChemBioDraw) is basically the MS Word of chemicals. Chem3d is the visualization package that's bundled. It's expensive (pirate it, shh) but from what I understand it's the gold standard, and for a reason too...
I also like Qutemol for making "print quality" renders and GIFs, like the Wikipedia articles for stuff like ketamine have.
If you just want to display 3d molecule files, RasMol is also good.
If you are a stickler for software licensing I believe that OpenBabel can also handle molecule editing and conversion (e.g. SMILES to MOL) but it does so from the command line.