This will get you started.
http://www.followthemoney.org/database/nationalview.phtml
http://www.opensecrets.org/orgs/list_stfed.php?order=A
http://www.google.com/url?sa=t&rct=j&q=corporate%20contributions%20to%20politicians%20info&source=web&cd=8&ved=0CGIQFjAH&url=http%3A%2F%2Ffollowthemoney.org%2F&ei=kNy2TueUNan9iQLhytVW&usg=AFQjCNFrs6HeLYLMJD7IiKCX7nMv9H6FZQ&cad=rja
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