I just saw at BlenderNation that AssistCG.com has created a Node Compositing Library. And even better, they are offering it as a free download, along with a pdf that explains how to use it. Very cool.
The library is composed of a nice selection of useful Node groups that can be appended into to your projects or even used as a study aide to poke at and explore.
This library presents node groups and files for color correction, rotoscoping, keying and other video compositing activities. Also there is a small set of effects which demonstrates work with library.