There's a new option to search for real estate: click on "show search options" and select "real estate" from the drop-down. The search results
Many real estate sites use Google Maps API and the first Google Maps mashup was HousingMaps, a site that displays Craigslist housing listings on a map. Last month, Trulia was one of the first sites that integrated Google Street View "to add efficiency to the real estate search experience and help home buyers discover more information about particular neighborhoods".
(The post was updated to reflect that the data is obtained from Google Base.)