San Francisco, Oakland, Santa Barbara in top 5
Realtor.com reports US home listings drop 21% from year ago
Trulia: Most markets on list hit by price declines near 50% or higher
Altos Research: More ups and downs ahead for house prices
South accounts for 6 of 10 metros with highest jumps in median list price
ZipRealty: Median list price falls 13% year-over-year
Share of 'underwater' homeowners at new peak