On my husband's recommendation, I downloaded Google SketchUp (free). Its a 3D modeling program that he's using for his wood working. I used it to layout my next quilt. In about an hours worth of time I drew the attached picture. The next time it should take less. The interface is not completly intuitive but its not bad either. You can also use it to help calculate the amount of fabric you need as it will tell you the area of your various shapes.
I can't wait to get started!