Phil Carter suggests that the US should take advantage of private military units that are cropping up in Iraq.
On the other hand, Mark Kleiman raises a number of concerns including:
Armed forces not subject to governmental control are a recipe for thuggery at best, assassination in the middle, and civil war at the worst.
This seems like a pretty good description of armed forces under government control. Well, perhaps, the last phrase should be modified to read: waging war at the worst.