I've always loved the main theme of Dragon Age: Origins, it always sounded so... well, epic.
http://youtu.be/oWFEVbfCcOY
The opening movie of Final Fantasy XII does it for me too. Probably because it combines some of my favourite FF themes.
http://youtu.be/szG8npbEmEA
The first Silent Hill has the monst sinister and brilliant track:
http://youtu.be/_EN-_1OGtUY
Argh, and I can't forget the start of VII either, with the zoom out of Midgar, then the zoom back in to the train and the whole time this music is just... Yeah.
http://youtu.be/u5Y6Sza8Nt0
Music is really important to me in a game, it creates so much atmosphere.
