FREE Geometry Shell Toon Outline (GSO) shader. UPDATED: May 19th 2013 - Additional Bugfix.
Update May 19th 2013: I recently discovered another issue with the Geometry Shell Outline (GSO). Although it was compatible with UberEnvironment's Ambient Occlusion, it wasn't compatible with lights casting Raytraced shadows. You had to turn "Cast Shadows" OFF to stop Raytraced shadows from reacting to it, which in turn stopped it from being compatible with UE's Ambient Occlusion. So, with the help of Richard Haseltine once again, a second Ray Test was added for Transmission this time. Now the shader is compatible with both Raytraced shadows (and presumably depth mapped shadows too) and Ambient Occlusion. Remember to keep "Cast Shadows" turned ON (this is the default setting when creating Geometry Shells).
Please note that the two Ray Tests the GSO shader does may increase rendering times. In my own tests using a complicated light set, rendering time increased by 1 minute when adding a GSO (and that minute was spent on calculations). It goes without saying that the more complicated and higher quality the light setup is, the longer the render will be. Although the GSO is now compatible with complicated light setups, it is strongly advised that you stick to simpler light setups especially when doing Toon work.
Please redownload and reinstall.
Update May 2nd 2013: With the help of Richard Haseltine, the Geometry Shell Outline is now compatible with UberEnvironment's Ambient Occlusion. The Geometry Shell Outline should no longer cause the underlying object to appear darker. If you are still having this issue, please make sure the Geometry Shell's "Cast Shadows" parameter is turned ON. Yes, I know, that doesn't make much sense, I don't fully understand it either, but that's the only way to make it work. :P
The Basic Guide has been updated to reflect this. Please redownload and reinstall.
This is a crosspost from my main Visual Style/Manga Style support topic, just to make sure you guys know it's there. I've taken the Geometry Shell Outline shader included originally with my Manga Style set on the Daz 3D store, made some improvements to it, and have released it for free!
Also, be sure to check out the official Manga Style & Visual Style topic for information and support on these two products, step-by-step guides on how to use them, as well as some freebie lights and render settings (Manga Style Freebie Pack 1).
Special Thanks: Gilikshe, and Richard Haseltine.