BioShock was up there. "Wouldya kindly..." But I have to say that the best was in System Shock 2, when:
The first time I saw that, I literally fell out of my chair.
you walk into Dr. Janice Polito's office, only to find her dead in a chair; then the walls drop away and SHODAN reveals herself to you: she has been the one guiding you all this time.
The first time I saw that, I literally fell out of my chair.