] Do you ever wonder where that paper money in your pocket
] has been, or where it will go next? This is the place to
] find out.
]
] All you need to do is enter the denomination, series, and
] serial number of any US dollar bill, and your current USA
] ZIP or Canadian Post Code

Ever run across a dollar bill with the "http://www.wheresgeorge.com" URL on it? Be sure to enter in the bill's serial number to this database before you spend the bill somewhere else -- this site tracks the flow of certain marked bills around the world. Fun!

Where's George? - Currency Tracking