Mortgage insurer PMI Group is forecasting lower housing prices by the end of March 2011 in 30 of the top 50 metropolitan areas. Forecasting algorithm uses a combination of price-appreciation trends, affordability, unemployment, interest rates and local economic conditions.

http://www.inman.com/news/2009/07/8/mortgage-insurer-ids-weak-markets

You can view a copy of the PMI research report at http://www.pmi-us.com/econ/index.html