Most housing indexes track broad geographic areas, so Manhattan's ritzy Upper East Side might be lumped in with gritty neighborhoods in Newark, N.J. The Forbes Luxury Housing Index tracks sales prices in the 500 most expensive neighborhoods by ZIP code. Prices will be updated weekly as new transactions occur. Below, areas with the largest median price declines and gains in the last year. More > % change: -0.17%current price: $1,258,811 Source: Altos Research New Jersey Suburb's Prices Holding Up Bucolic Mendham, N.J., again leads this week's list of biggest gainers. Home Of The Week: Mendham Mansion This confident, traditional brick property rests on eight acres of wooded land just miles from New York City.Biggest Drops Place Price April 27, 2009 % Change From 2008 Mendham, NJ 07945 $1,260,507 9.84% Wellesley, MA 02482 $1,239,961 10.45% San Mateo, CA 94402 $1,191,307 10.52% Great Neck, NY 11021 $1,398,326 11.20% Pasadena, CA 91105 $1,386,923 11.47% Biggest Gainers Place Price April 27, 2009 % Change From 2008 Marina del Rey, CA 90292 $1,808,653 -31.70% Rumson, N.J. 07760 $1,340,953 -30.72% Dana Point, CA 92624 $1,025,146 -28.39% Los Angeles1, CA 90019 $583,723 -27.20% Sunnyvale, CA 94089 $427,149 -26.92%