What are in your opinion/experience the greatest video game moments/scenes?

Mine:

Battle with Psycho Mantis (Metal Gear Solid)



I remember the first time I and my brother fought Psycho Mantis, it was, in a way still is, unlike any other boss battle. The entire scene, reading your memory card to find out which games you play, "moving" your controller, was impressive at that time. It took us quite some time to figure out how to defeat him.

Sovereign (Mass Effect)



The entire speech is epic to say the least. It made Reapers even more mysterious, even more menacing, from that point on I just wanted to find out as much as possible about Reapers... then starchild came and pooped all over it.

That will have to do for now.