The title says it all so I'll go with Final Fantasy X or The Hitman Series
Shadow of The Colossus (Wander and the Colossus- Roar of the Earth)
Final Fantasy VI-IX Original Soundtracks
Final Fantasy VI Grand Finale
Any misc Final Fantasy Concert CD (more friends, etc.)
The Orchestral Game Concert series
Metal Gear Solid series
Silent Hill series
The Darkness (No official soundtracks but I've found game rips.)
Alone in the Dark (The recent awkward current gen game had a fantastic soundtrack.)
Castlevania: Symphony of the Night!
Devil May Cry has some good tracks among it's soundtracks. Recently I've been listening a bit to FFVII: Crisis Core, there seems to be some excellent music in there. Like what I've heard from both Bionic Commando next gen and Re-Armed. Oh, and Braid's music is amazing too.
just that one metal song that kicks in every time you fight.
nah but seriously, Oblivion, GTA4, Bad Company to name some recent favs.
Braid soundtrack is pretty good, it suits really well to the games art design, and sounds appropriate when you start rewinding time.
I like classic video game music. I can't think of any games that have come out in the past 10 years where I've liked their original music. Yeah, gta usually has good music but that's not the same.
My favorites are Mega Man 2, Super Metroid and Mega Man X. I play Mega Man X mainly for the music.