(FORTUNE Magazine) – This election cycle, 527s have replaced PACs as the political money-handlers du jour. Groups like MoveOn.org, Swift Boat Veterans for Truth, and a new group running ads that attack Bush's military record, Texans for Truth, have all generated headlines as well as controversy. Reformers argue that 527s (tax-exempt groups that are free to use soft money for any political purpose except for explicitly backing a candidate) violate the spirit of campaign-finance reform, while proponents say the ads are just free speech. So who is speaking the most freely? Despite all the press about the Swift Boat Vets, it turns out that most of the biggest 527s are left-leaning--though the Swift Boaters have been growing fast. Here are a few of the major players and a couple of small groups that are making a big splash. -- Kate Bonamici