Yesterday, Trulia, the real estate search startup, and one of the oldest mashups on this site, just announced their new API. This REST-based API provides access to two primary types of data: local real estate price trends and real estate search behavior online. It should lead to some very interesting mashups.
This release is also notable as a showcase for API management provider Mashery who are providing Trulia with API infrastructure, rate limiting, developer community, and other related services (see our earlier coverage of Mashery here).
Some more notes of interest on this: