Currently the only real resource for Cell Shading renders is to use pwToon’s Shaders with some old free shader presets by Crescent that take a good amount of adjustment to work. I don’t know what the market is for this kind of thing, but it’d be nice to see some high quality Cell Shading shaders!
With appropriate set of lights, PWtoon + Crecent work fine. Image (1) and (2) were created with this combo.
But a very intensive set of light can be a problem. I’m working with a shader for cell shading that control global light intensity, global light tone, shadow coverage, and others. Image (3) and (4-5) are an example from my work. It must consider that it is in a very early stage of development.