I admit, my knowledge of celshaded plugin renderers is mostly limited to LightWave, however, I'll post links to what I've found.

B.E.S.M. -- Big Eyes Small Mouth This celshader was originally developed for LightWave, but recently they released the code as open source. Anyone can download the source code and develop it as they see fit (very kind of the author).

UnReal Extreme - Celshader Another LW plugin. This website is in Japanese, so if you can't translate it (I can't!) then it may be hard to navigate.

Illustrate 2.0 Celshader This one isn't free. It's also for 3ds max.

I've tried finding some for Cinema 4D. From what I hear there aren't a whole lot available. Some are in development, though. However, Cinema 4D does come with some good built-in support (again, this is what I've heard - since I've only used the demo, I can't speak from experience). Here's the link to a thread at CGTalk which is about Cinema 4D's cel shading capabilities. CGTalk Thread about Cel rendering in Cinema 4D

From experience, I've only used LightWave's built in celshaders (SuperCelShader and BESM). That, and SketchUp. It's hard to find a shader that's universal to many applications. That's why it's so exciting to watch what they did in those videos from their research. It seems very hopeful that the solution they're researching will become a shader that can be used with any application.