Hmmm. Top-100 donors to political candidates and political parties, 1989 to 2009 (400k PDF). Source: www.opensecrets.org
UPDATE 11.09.11: Of the top 20 recipients of labor campaign cash this cycle, only two are Republicans, take a look.
Click-through to see it better. The political Left is always ranting about getting the money out of politics, but a great deal of it seems to be coming right from their own backyard.