Yes there is oversight by the House and Senate Intelligence Committee to which the President's National Security Advisor and several other high ranking officials in the intelligence world are required to give briefings. The President cannot do anything without the eventual approval and oversight of Congress. For example, even the Presidental War Powers Act only permits the President to wage war for a short period of time before getting to approval of Congress.

The problem for Congress with the "war on terror" is that they gave the President almost blanket approval to fight the terrorists without any specific defined goal of victory which would call an end to his power to wage this war. Because there is not a well defined enemy such as in the case of WWII the President could in theory wage the war on terror indefinitely or until the Congress passed a bill repealing his power and Congress was then able to also override the President's veto of that bill (which is exactly where we seem to be headed this week although the Congress does not have the necessary votes to override the coming veto.)

As to the whole issue of Executive Orders, legally it is extremely questionable as to whether or not they are even constitutional. There is nothing in the Constitution that explicitly gives the President the power to issue executive orders and more importantly there IS a provision in the constitution that expressly reserves the power to make laws to the Congress.