Housing prices dropped by the biggest rate ever in May, down 15.8% compared with a year ago, according to Standard & Poor’s/Case-Shiller 20-city index. The 10-city index dropped 16.9%, the steepest decline in its 21-year history. Nine cities posted records lows in May–Las Vegas, Miami, Phoenix, Los Angeles, San Diego, San Francisco, Seattle, Wash., Portland, Ore., and Washington, D.C., and the value of housing in Detroit is now lower than it was in 2000. Seven metros showed smaller annual declines–Tampa, Fla., Boston, Detroit, Minneapolis, New York, Dallas and Atlanta–a possible bright spot in the data. The city with the...