This is one of those effects you won’t be using very often (if ever), but it’s useful to learn more about the compositor and open to new ideas. This tutorial is based on 2.68 and uses Cycles (but can also work with BI).
Difficulty: Intermediate (you should know your way around Blender)
Delete that wimpy default cube and add a Monkey to the scene. Rotate it so it’s facing the camera, then rotate on the X axis so it’s looking slightly downwards. The latter is a matter of style, you can do whatever you want. Now, we need darkness to appreciate light so go to the properties panel and set the world background color to pure black.