Well, here's an idea: leave Najaf the hell alone. We all know what happened in Fallujah, right?
Sure, its possible to retake the city, but there's gonna be
a) a hell of a lot of dead civilians
b) a hell of a lot of dead insurgents
c) a hell of a lot of property damage, religious and otherwise
d) as a consequence of a, b and c, a hell of a lot of angry Iraqis (and Muslims in general)
Isn't it obvious by now that the country can not be won by force. And that whole hearts and minds deal is about as likely as Elvis comeing back from the dead for another album. And Iraqis are very quickly wising up to the fact that Allawi might not really have their best intentions at heart (his office was recently torched).
Every dead Iraqi bring the US closer to defeat, not victory.