On PopSci's Best of What's New 2005, check out Grancrete:
Grancrete descends from a product developed to encase radioactive waste. And since it takes hours instead of weeks to build a home, itâ€™s poised to provide low-cost, high-quality shelter to the estimated one billion people who lack it. $20.50 to coat 15 square feet.
[Thanks to John for the link.]