A great little interactive tool compares house price trends to income trends and general price levels for twenty countries. Be warned that it is flash-based. Most series seem to go back to 1990. Relative to incomes, Holland and Belgium show the greatest increases, while the big decliner was Japan. Thanks to Steve Keen for finding it and providing the link, originally from The Economist. And of course we know that house prices mainly represent the cost of land (including the cost of permission to build).