I just got this binding tool, and it's wonderful. It solves that problem of the last stage of the binding when you're estimating how long to make the tails so that they fit snugly around the edges. I have to guestimate and baste several times to get it right, but this tool makes it work the first time perfectly.
The company says: The Binding Tool
When you finish the last seam of the binding only an angle seam will work to reduce the bulk of this last step. The Binding Tool makes a perfect ending every time. Two measurements and two cuts and you’re on your way to a great finish.
Company web site: http://quiltersmerc.com/simpl-ez-rulers.aspx
Demonstration: on YouTube: www.youtube.com/watch?v=DAGrGz6ukn0