Taiwan's Micro-Star International (MSI) recently demonstrated a power design that can cool a PC motherboard without electricity. The design employs a fan that is powered only by the movement of heat and air, using an approach known as the Stirling Engine Theory. It is named for Robert Stirling, a Scottish pastor of the early 1800s who grew concerned about the danger workers in his parish faced from steam engines of the era, which were prone to explosions. He invented the heat economizer, which uses hot air rather than steam.
In MSI's demo, the "Air Power Cooler" transfers the chipset waste heat into air momentum. As the air becomes hot, it exerts upward force on a piston, which in turn drives a fan that cools the heatsink. The company demonstrated the technology recently at the CeBIT technology show. Can it scale to handle higher heat loads? See Hexus and Tweaktown for more details. There are also YouTube videos of an animation illustrating the concept and a brief clip of the unit in action (it's about 25 seconds into a longer MSI CeBit promo).