The Iraqi people
The first clear winners given today's events are the Iraqi people. For the first time in their history, they looked tyranny in the eye, and tyranny flinched. They have also put the lie to the assertion that Muslims and Arabs in particular are incapable of Democracy and have added yet more weight to the assertion that freedom lives in every human heart regardless of race or religion.
President Bush and the US more broadly
Today's events vindicate, at least in part, the vision that the President put forward in his inaugural speech. They also show that Iraq is on an almost unstoppable course toward democracy. The next two votes in Iraq, the one on the constitution 9 mouths from now and the Presidential election in about a year, will solidify this course. This will effectively end the insurgency. If you don't believe me just ask Abu-Musab al-Zarqawi:
if we fight them, that will be difficult because there will be a schism between us and the people of the region. How can we kill their cousins and sons and under what pretext, after the Americans start withdrawing? The Americans will continue to control from their bases, but the sons of this land will be the authority. This is the democracy, we will have no pretext.