Ezra Klein prepares the bill:

The Afghanistan and Iraq wars, neither of which would’ve been launched without bin Laden’s provocation, will cost us a few trillion on their own, actually. … [W]e’re well into the trillions, and when you add in the cost of the oil shock and its potential contribution to the credit bubble, we’re talking about many trillions indeed. Has any single individual even come close to costing America that much? Adolph Hitler is probably one of the few candidates, but I’d argue that World War II was a lot less about him than 9/11 was about Osama bin Laden. And who else is even in the running here?