If your talking emotional or classical scores, I LOVE Final Fantasy XII’s soundtrack. Similarly Tactics too, its the same guy. A lot of Final Fantasy music is classic, but XII to me makes the game. Farming enemies for long periods of time isn’t so bad because the music is great.
Chrono Trigger’s is great.
Action games, the entire Mega Man mainline series soundtrack for me. Especially X1, X4, 2, 3 and 7.
I’m not a good fighting game player (combos or online anyway), but Street Fighter and Marvel vs Capcom soundtracks are awesome too. BlazBlue’s soundtrack is phenomenal.
While not widely known in the west, the Super Robot Wars franchise is chock full of fantastic music. Both licensed from anime and original tunes.
Fun fact on that Transformers Soundtrack. I swear its either a generic mix of sound loops or it has been licensed out, because I SWEAR I hear that very soundtrack in the background of a show on History Channel, I think it was. It was good, though.
A soundtrack to a sadly under-loved game I REALLY want to get a copy of is Alundra. Oh my god does that game, and it’s soundtrack, hit you right in the nuts.