I’ve used some 2dFilters, (bloom, glow, etc) but when I was searching for more, I found in blenderartist forums an interesting filter, the author (I can’t recall the name right now, sorry man!) called it “Cheap Normal Effect“, and I liked the fact that I provides with some kind of toon/stroke effect. If you want to try it, check the link here, and attach it to a custom 2dFilter sensor.
This is a old game project video, just found the video in my screen capture folder and decided to do some editing just for fun.
The entire level is a “proxy” model, the final one was intended to be more detailed, so this one was for testing purposes.