Since black roof tiles absorb heat and white ones reflect it, we should all just plain re-do our roofs biannually to save energy as the seasons change. Or maybe just get roof tiles that change color on their own.
A bunch of MIT students came up with this funky-looking roofing material, dubbed Thermeleon, which changes color based on temperature. According to initial studies, "in their white state, the tiles reflect about 80 percent of the sunlight falling on them, while when black they reflect only about 30 percent." This would translate into about a 20 percent saving on cooling costs in the summer.
Pretty neat, but unfortunately there are no plans to commercialize the tiles yet, and even if there were you'd probably have quite a battle with your home owners association to install them. [MIT News via Gizmag]