I mentioned learning about Three Point Lighting at the Videomaker Conference I attended. While looking through some of the Videomaker tutorials, I ran across this one that demos the process. While videos and diagrams are helpful, I still found watching someone do this in the flesh to be an invaluable experience. If you ever get a chance, have a knowledgeable person demonstrate the set up and describe what each of the three lights are supposed to do.
The three articles Mark mentions at the end of the video are bookmarked here for your, and my, easy reference.
Illuminations: Why Three-Point Lighting?
Illuminations: Applying 3-Point Lighting
Light Source: Lighting Women/Lighting Men
[Image: "I know I'll never have to turn that light on again": Flickr: Uploaded on January 24, 2006 by eqqman: http://www.flickr.com/photos/eqqman/90571238/]