600,000 excess deaths in Iraq since U.S. invasion
This implies that about two hundred (200) times as many extra Iraqis have been killed since the U.S. invasion as the number of Americans killed on 9/11. While most of the deaths in the first year were attributed to the U.S.-led forces, most of the deaths since are attributed to insurgents. The study controlled for reporter bias by checking actual death certificates and finding them in 92% of the cases -- pretty good record-keeping and truth-telling for such a chaotic land.
Here is the study. Here is a good discussion of the study.