Donnie Fowler, son of former DNC chairman Don Fowler, one-time Wesley Clark campaign manager, and chief of John Kerry's Michigan campaign, is currently the most aggressive candidate for the DNC chairmanship.
Aggressive in that he's announced his candidacy, has a website, is calling not just DNC members, but just about everyone he knows in politics (including every former Clinton staffer, whether they have a vote or not). At the Orlando cattle call a couple weeks ago, Fowler was the only candidate in attendance in full campaign mode, with lawn signs, buttons, stickers, etc.
If you don't know anything about Fowler but would like to learn more, you could do worse than watch this C-SPAN interview in Real Player.
Fowler is running as a reform candidate. Whether his rhetoric checks up against his history remains to be seen, but he's not someone who should be dismissed outright (unlike, that DLC-minded, energy industry lobbyist Jim Blanchard).