WunderKat, a new method of energy production:

The novel approach is based on two common but previously unexploited natural laws.  One is a well-known form of Murphy's Law which states that when toast is dropped, it always lands buttered side down.  The other law states that when a cat falls, it always lands on its feet.  These two laws are set in opposition to each other by attaching a buttered piece of toast to a cat's back, buttered side up.  If the cat is then suspended in the air, the two laws cause the cat to perpetually rotate.  By building a device to hold the cat and capture this rotating energy, enough force is harnessed to drive an electric generator. 

(via Neatorama)

Update (2007-04-12 9:29am):  I've learned that this is called the Buttered Cat Paradox.