Our API directory now includes 40 real estate APIs. The newest is the XWeb Real Estate API. The most popular, in terms of mashups, is the Zillow API. We list 28 Zillow mashups. Below you'll find some more stats from the directory, including the entire list of real estate APIs.
Related: Top 10 Mapping APIs
In terms of the technical details, REST and XML lead the way. There are 28 real estate REST APIs and 5 real estate SOAP APIs. Our directory lists 28 real estate XML APIs and 19 real estate JSON APIs.

The most common tags within real estate are 9 real estate search APIs, 4 real estate mapping APIs and 3 real estate UK APIs

On the mashup side, we list 245 real estate mashups. We named Real estate mashup as mashup of the day in October. For reference, here is a list of all 40 real estate APIs.
Agent Storm API: Real Estate systems connection.Track this API
AgentRank API: Real estate agent sales, forecasts, and reviews.Track this API
Daft API: Irish real estate site.Track this API
Dezrez API: Real estate listing service.Track this API
Fizber Neighborhoods API: Neighborhood data service.Track this API
ForeclosureListings.com API: Real estate foreclosures.
Home Hippo Property Portal API: Online real estate Portal.Track this API
HomeFinder.com API: Real estate listing service.
Idealista API: Spanish real estate portal.Track this API
ImmobilienScout24 API: Real estate search in Germany.Track this API
ListingWare API: Listings Search Service.Track this API
National Buyer Listing Service API: Real estate buyer data sharing service.Track this API
Nestoria API: UK real estate listings.Track this API
New York Times Real Estate API: Real estate listings and sale prices.Track this API
Onboard Informatics API: Real estate listings and search service.Track this API
Onboard Lifestyle Search API: Real estate listings and search service.Track this API
Onboard Points of Interest API: Real estate listings and search service.Track this API
Onboard Property Search API: Real estate listings and search service.Track this API
PeekaCity API: Location-based services.Track this API
PetaProperti API: Indonesian real estate service.Track this API
PlanningAlerts API: Alerts service for UK local planning alerts.Track this API
Public Transit Score API: Real estate transit score service.Track this API
Real Estate Cloud MLS API: Real estate multiple listing service.Track this API
Realtors Property Resource API: Real estate data service.Track this API
RealtyBaron Agents API: Find a real estate agent service.Track this API
RealtyBaron Answers API: Real estate question and answer service.Track this API
Rentometer API: Realestate pricing services.Track this API
RentRange Rental Rate API: Real estate pricing service.Track this API
RentRent API: Craigslist rentals data service.Track this API
REVO API: Real estate listing and promotion Platform.Track this API
Rezora API: Online Marketing for Real Estate Professionals.Track this API
StreetEasy API: New York Real Estate search and information.Track this API
Trulia API: Real estate search.Track this API
ValueAppeal API: Property Tax Appeal Service.Track this API
Walk Score API: Real estate walk score service.Track this API
XigniteHousing API: U.S. housing market statistics.Track this API
XWeb Real Estate API: Mortgage loan application service.Track this API
Zillow API: Real estate pricing and valuations and mortgage rates.Track this API
Zoopla API: Property and real estate search engine.Track this API
ZooProperty API: Real estate listings and data hub.Track this API