Like some other people, I have too many to pick one, so here's all the ones I can think of now.

Terra's theme - FF6
To Zanarkand
The song during the MGS credits
MGS2 theme - epic, pure and simple. I still remember watching the original trailer for this game 30 some times and loving it and this song more each time.
Snake Eater - MGS3 (I thought it was surprisingly perfect during the fight with Boss)
Simple and Clean