I like this a bit better than the cheap jig I made. The author basically takes 2 pieces of angled metal, and makes a guide out of it for the saw. Good way to cross-cut wood too. I have been interested in track circular saws, but at $500 for a good one, I have stuck to cheaper solutions.
http://www.instructables.com/id/Get-More-from-Your-Circular-Saw/