Real estate web service Zillow has progressively made a large amount of information available via its API (our API profile). Recently the Zillow API was updated to include access to additional information, including GetRegionPostings and GetUpdatedPropertyDetails API calls.
According to the Zillow blog:
The GetRegionPostings API takes a place (ZIP code, neighborhood, or even geo points) as an input and returns a count of listings by type (Make Me Move, for sale by agent, for sale by owner, and reported for sale) in addition to some home facts about each property returned.
The GetUpdatedPropertyDetails API call provides property details for home facts that have been edited by the home's owner or agent.
Other web sites have mashed up various types of Zillow data available via its API, including city and neighborhood information (regional home value trends, demographic data, and other data about homes). Education.com and Banks.com have both tapped into city trends and demographics to provide value-added result listings.
Although not available via its API, Zillow has made neighborhood boundaries data available to the public via a Creative Commons license. Check out walkability ranking web site Walk Score, which uses this data in conjunction with heat maps, and Andrew Mattie's blog post on how to use the neighborhood data to build a mashup in 24 hours.
We currently have fifteen other Zillow mashups listed in our mashup directory and we look forward to adding more mashups as developers continue to tap into the broad set of data available via the Zillow API.