Over the past few years, we have become all too familiar with housing bubbles. When markets go bust, it gets ugly. Rapidly rising home prices in the early 2000s got the U.S. and parts of Europe into lots of trouble; these economies slumped into recession when prices crashed. Nobody wants to relive another economic disaster, but in some parts of the world, housing markets are looking bubbly, and some fear they risk putting economies in jeopardy. Here's a look at five markets to watch.