The Center for Responsive Politics (CRP) is a non-profit, nonpartisan research group based in Washington, D.C. that tracks the effects of money and lobbying on elections and public policy. It maintains a public online database of its information.
Their database OpenSecrets.org allows users to track federal campaign contributions and lobbying, by lobbying firms, individual lobbyists, industry, federal agency, and bills. Other resources include the personal financial disclosures of all members of the U.S. Congress, the president, and top members of the administration. Users can also search by ZIP codes to learn how their neighbors are allocating their political contributions.
Source: Wikipedia: http://en.wikipedia.org/wiki/Center_for_Responsive_Politics