Federal Election Commission Campaign Guide: Corporations and Labor Organizations
OpenSecrets.org - a non-partisan, research group which tracks money in politics and its effect on elections and campaign finances; use the Donor Lookup database to find out who has contributed to candidates. (Center for Responsive Politics)
Follow the Money offers close-to-home data and information on the power of influence (National Institute on Money in state Politic)
Campaign Finance Data - Financial disclosure reports from Presidential and Congressional campaigns, political parties, and PACs.
Search the Colorado Campaign Finance Database for local candidate financial disclosures.