Depending on what kind of panel you have, the manufacturer may have a template available on their website. However, it's probably just as simple to make one up in Word or whatever word processor you happen to have on hand.
Bigjohn2,
I helped my son upgrade his electric in his house and just went through this. There are many templates avaiable to use. Just google electric box label template and choose the one you think will work the best for you.