Real estate API services from zillow.com
The Zillow API is Zillow's service that allows preapproved licensees to retrieve certain data relating to residential real estate and mortgages ("Zillow Data"). The Zillow API consists of multiple application program interfaces for retrieving various types of Zillow Data, grouped generally by the type of data being retrieved, and includes, without limitation, calls to retrieve valuation data (the "Home Valuation API"), calls to receive attributes about particular properties (the "Property Details API"), calls to receive information about mortgage rates (the "Mortgage API"), calls to receive information about homes posted for sale (the "Postings API"), and calls to receive information about real estate professionals (the "Reviews API" and the "Directory API").
Zillow's real estate data is useful for turning a website or services into a real estate portal. http://www.zillow.com/howto/api/APIOverview.htm