One of the most memorable COD missions is a reverse escort quest
That was fun. They pushed some of those missions a bit too much in later CODs though.
I think another nice twist on escort quests, would be quests where you are "escorting" specific NPCs from afar, by covering them with a sniper rifle or helicopter, or heck, a bow and arrow. I'm sure there are some examples of that, but I don't remember any off-hand. Usually the COD "overlord" missions were more shooting fish in a barrel type of fares, rather than focusing on covering specific individuals even if that was ostensibly what you were doing.