The Petfinder PHP SDK by Brian Haveri allows to communicate with the API to implement animal search features into applications. Brian provides the instructions to download the PHP library, obtain a developer key, and run the code.
An email address can be the key to an online identity, and that's just what IDLight is using in its identity lookup API. By supplying either an email address or a URL to the IDLight API you could be turning the key to unlock a swath of identity information.
ResultR deserves mention as it's a meta search engine mashup built by two self-described "Web 2.0 Kids" as a high-school project. With it you can create your own search engine by choosing from 30+ sources you might want to include in your results.
Yahoo has taken a major step in the evolution of search APIs with today's release of BOSS (Build Your Own Search Service). The BOSS platform lets developers build their own full-blown custom search applications on Yahoo's index of the Internet, the same infrastructure that underlies Yahoo Search.