The White House has announced that Petitions 2.0, the platform code for the We the People website, is now in development and includes an API that will be released to the public in the coming months. The first set of API calls will be read-only and will be released in March 2013.
The Socrata Data API or SODA is one of the foremost API resources for Government and for social data discovery. One of the major use cases for open data is of course increasing law enforcement effectiveness for analysis and transparency. One such mashup using the Socrates API is the Crime Data for San Fransisco.
Now you can use an API to find out once and for all whether you are among the living. The U.S. Social Security Administration maintains a "death index" to prevent fraud. CDYNE Corporation subscribes to the updates and has opened the index up with a fee-based API (details at our Death Index API profile).