I like to look at the Freakonomics blog from time to time.  Recently they ran a contest to
come up with the best 6-word motto for the United States.  The top five
mottos, and the number of votes for each, are as follows:

Our Worst Critics Prefer to Stay (194 votes)
Caution! Experiment in Progress Since 1776 (134)
The Most Gentle Empire So Far (64) votes
You Should See the Other Guy (38)
Just Like Canada, With Better Bacon (18)

I like 1, 2, and 5.  I wonder if bumper stickers are already available.