Blender 2.72 introduced the sun beams node in the compositor. It comes in really handy when creating light rays. Since it is a pure post-pro effect, it can even be applied to images.
You can use Blender to make footage look like it was shot in 1920, by using particle systems and the compositor. Here is how:
Jonathan Lampel shows you how to create custom lens flares in Blender using only the compositor. The result can even be used as a group node.
A stencil for an animated background is a nice element for motion graphics. Unfortunately, the compositor is not always well-suited here. But Cycles comes for the rescue!