Excellent source for data on federal, state, and local campaign contributions, lobbying and political spending. Pulls together data from multiple sources.
Follow the Money is run by a non-profit organization.
Learn more about their funding here.
Includes the following candidates and elections:
• State offices, including courts (2000-present)
• Local offices (2006-present)
• Ballot measures (2000-present)
• President, Senate, and House of Representatives (2010-present)