Here is an example of the one I created!
Here is the website! Enjoy: http://www.keepcalm-o-matic.co.uk/default.aspx#createposter
UPDATE 9/18/2012-This post has had MAJOR hits. Thank you all for visiting and featuring on your pages. I can't take credit, I just happened to be one of the first who stumbled upon this awesome site.
LAST NIGHT I DISCOVERED A KEEP CALM APP FOR THE IPHONE. YES IT'S ADDICTIVE.
http://itunes.apple.com/us/app/keep-calm-carry-on-original/id393497171?mt=8 It does cost .99 cents but it's well worth it.