For those of you who don't want to make your own, a company called "Heartland" has this type of setup on sale right now at their closeout price of $16.99 at this site:
http://www.heartlandamerica.com/Item....asp?SKU=20191
If you have a pickup, there is a mirror that you can buy that clips onto the tailgate which tips down to show you where you're lined up. I think we got it from Cabela's, or Northern Tools.