A nice clip on something I've been following for years:
http://watch.discoverychannel.ca/dai...10/#clip298008
These guys built a wind powered cart that can go down wind faster than the wind.. so if the wind is 15km/h the cart can go 30 or 40 or whatever.
Pretty cool and completely counter-intuitive, as usual they even get the basic description wrong. The wind doesn't turn the prop to turn the wheels, the wheels power the prop which turns against the wind ("blows" against the wind).
One thread with lots of info for those interested:
http://forums.randi.org/showthread.php?t=173124