In the latest Strategy Page Iraq update there is a brief profile of the militias:
…One of the key decisions the government-that-doesn’t-exist-yet has to make, is what to do with the Shia and Kurd militias. There are two each, and the two Shia militias, those of the Badr and Sadr organizations, both backed by Iranian factions, are the most dangerous. The Shia militias represent Shia political parties that want to run the government. Not a democratic government, but a religious dictatorship
The two Shia militias are basically religious gangs, whose crimes are now seen as more of a problem than the declining violence of the Sunni Arab terrorists. For nearly three years, these Shia religious radicals were considered an asset. While the Shia radicals in southern Iraq are protected by the 10,000 armed men of the Badr Brigade (a part of (SCIRI, or the Supreme Council for the Islamic Revolution in Iraq), a smaller, but similar organization exists in central Iraq. This is the Mahdi Army, led by Muqtada al Sadr. This group tried to fight the U.S. forces, and lost big time. The Mahdi Army only has a few thousand armed men, and they have made themselves very popular in the Shia community by fighting the Sunni Arab gangs and terrorists that went after the millions of Shia Arabs living central Iraq. There are several other small Shia paramilitary organizations in central Iraq, most of which could be described as local self-defense forces. There is one exception, and these are police battalions recruited from Shia Arab areas and usually led by Islamic conservatives. The most notable of these is the Wolf Brigade, a force of some 2,000 well trained and disciplined police. These have been used in operations in Sunni Arab areas, to find and arrest or kill terrorists.