Just in time for the next election season, the team at MAPLight.org offer the MAPLight.org API which enables developers to "illuminate the connection" between money and politics by providing detailed funding information for candidates for political office. It's a growing data set and currently MAPLight covers candidates for the U.S. Congress, presidential elections, and the California Legislature.
The API is constructed using standard REST protocol with data results returned in XML format. In order to use the API, you need to know a candidate's Federal Elections Commission (FEC) ID. MAPLight provides a link to a tool for looking up FEC IDs on its API home page.
For example, the FEC IDs for presidential candidates Hillary Clinton, John McCain, and Barack Obama are P00003392, P80002801, and P80003338, respectively. Given the FEC ID's, you can easily obtain today's campaign contribution information for each candidate, using this request:
The MAPLight API is part of an emerging trend where mashups and APIs are developed to aid citizens in monitoring government and its workings. You can find more examples in the Government APIs and Mashups Dashboard.