Whether you want to "end the war" or raise the price of oil, driving a wedge between the U.S. and the Saudis would be the best way to start.
Eventually, as we move on from Afghanistan to other countries, the Saudis will start to get squeamish (as will the Eurotrash and "liberals" here in the U.S.). They will be increasingly fearful that we will not defend them when Saddam and Syria start trying to blow them up.