GameDev: How to 'Cel Shade' Your Games

"In an era of increasingly realistic game graphics, buzzwords like bump-mapping and per-pixel lighting take all the glory. The programmable hardware in today's consumer graphics cards does make these highly-realistic techniques available in real-time, but this same hardware makes stylized rendering available as well. Non-photorealistic rendering (NPR) is a branch of 3D graphics that has yet to be fully tapped for game use. With the advent of programmable shaders, a whole range of NPR styles are available that previously existed only in the pre-rendered domain."