That's a tough one...
Chrono Trigger (favorite soundtrack ever, and OCRemix's Chrono Symphonic album is some of the best orchestral music you will ever hear)
Final Fantasy VII (the most varied soundtrack I have ever heard, and with songs like One-Winged Angel and Aerith's Theme, just... yeah)
Final Fantasy VI (great soundtrack, and easily my favorite boss battle theme of the series)
Halo Series (for really knowing how to get the blood pumping, as well as having some beautiful slower pieces)
Shadow of the Colossus (for perfect mood-setting music and epic music befitting of the current state of each battle)
Inverse Skies said:
Super Mario Galaxy because of Good Egg and Gusty Garden Galaxy, beautiful orchestrated songs which are amazing to listen too.
ME TOO!!! Even those two particular songs: they and the ending credits music are my favorites! I was so surprised at how much I fell in love with that soundtrack...