An airplane, created at Georgia Tech. recently took a test flight that may go down in history.  The plane, an unmanned vehicle with a 22 foot wing span, was powered entirely by a 500 watt, compressed hydrogen fuel-cell. 
It couldn't have been particularly easy, as most planes require much more than 500 watts, and we'll have to wait a while before one of these things can carry a person around.  But it's a first step towards greening a terribly necessary, but terribly fossil-fuel dependant sector of our economy. 

The vehicle runs on compressed hydrogen, which is much less expensive and easier to work with than liquid hydrogen, which has powered UAVs in the past.  How easy is compressed hydrogen to work with?  Well, the hydrogen was stored in a tank designed for paintball guns, a fairly inexpensive technique.  As they continue to modify the design, they hope to build a compressed hydrogen powered UAV capable of trans-Atlantic flight.