I can has?
US debt is projected to reach $15 trillion by the end of this year. How much is that, really? Well, this site has some visualizations using standard $100 US bills. It's computer-generated -- there isn't actually enough printed US currency in the world for this exercise. In 2008 all in-circulation US bills had a face value of around $850 billion (all denominations). Interestingly, according to the latter link, there's over $16 billion in US pennies in circulation (1.65 trillion pennies at $0.01 each, obviously). Who says pennies aren't worth anything? :-)