One existing molecular viewer which influenced my views on Avogadro
is called “iMol” for Mac and “Biodesigner” for Windows:
http://pirx.com/iMol/
http://pirx.com/biodesigner/gallery.html
The programs themselves don’t offer much in the way of "editing"
functionality, but do offer a range of nice graphical output, labels/
monitors, selection, etc.
I recently e-mailed the author to ask about iMol – at one time he
had said he was thinking of making it available under the GPL. He
said that he was working on a new version using the FLTK toolkit to
make it more cross-platform and forwarded me to a new picture gallery:
http://www.pirx.com/bio_gallery/
Really nice, actually.
In a similar vein, I’ve come across a few other sites which were
interesting:
-
QuteMol uses procedural rendering with ambient occlusion to handle
depth effects
http://qutemol.sourceforge.net/fxs/
http://qutemol.sourceforge.net/sidetoside/ -
American Scientist magazine (a journal for the Sigma Xi
scientific society) had an article on “adaptively sampled distance
fields” for molecules:
http://www.americanscientist.org/template/AssetDetail/assetid/
53064#53435
Some nice eye-candy for the evening. 
Cheers,
-Geoff
