FF VII - I just love it when you leave Midgar for the first time and it pans out to show you just how little of the world you've seen - absolutely breaktaking.
Tomb Raider, when you climb to the top of the Sphinx and the camera pans away to show you how high up you are - you do go higher in the game, but that was the best one.
WoW - there have been some big bosses in the game, but Ragnaros is one of my favourites, with Majordomo Executus announcing his arrival, then this omgwtfbbq huge flame pillar springing up out of the lava - epic.
CoD4 - when you get caught in the nuclear explosion - that was brilliantly done, I was actually choked up by that scene.