This is the one we used (although we have modified our own by also printiing the Cache Name if we know it beforehand and we have also added "Cache #-- by Peter and Gloria")
I just make something up with one of my many graphics SW packages I have. I've used Paint Shop Pro, CorelDraw, MS Works Home Publisher, MS Word or Star Office. Pretty much any SW pakage that can create fonts with colors should do the trick.
I usually download a logo either the website of geocache.com or MBGA logo and include it somewhere.
This question has come across my little mind as well, thank you for the answer! I also hope that it is ok that I printed a couple off? The Cache is still yet to come...