It may not be the most widespread measure of housing prices, but if you want to follow a powerful driver, look at rents. Specifically, it's the rents Americans pay on condos, apartments or houses that are about the same size, and share the same neighborhood as your ranch or colonial, that in the end determine what your house is worth. "If you look at the trend in rents to see where housing prices are headed, you're looking at the right measure," says Yale economist Robert Shiller.