Hmm. A very difficult quesiton for me to answer, considering I have so much music from my GamingFM days and I've continued to addd to my collection in all that time.
Some that stand out to me:
Final Fantasy IV
Final Fantasy VI
Final Fantasy XI
Final Fantasy XIII and XIII-2
Ninja Gaiden (8 bit) I and II
Castlevania (8 bit) I, II and III
Super Castlevania
Castlevania: Rondo of Blood
Castlevania: Dracula X Chronicles
Castlevania Symphony of the Night
Castlevania Harmony of Despair
Castlevania: Lords of Shadow
Real Bout Fatal Fury
KOF 94
KOF 2000
The Last Blade II
Dragon Warrior (any)
Devil May Cry
Devil May Cry 3
Shin Onimusha
God Of War I and II
Shadow of the Colossus
Tales of the Abyss
Legend of Zelda I and II
Legend of Zelda: Ocarina of Time
Legend of Zelda: Majora's Mask
Legend of Zelda: The Wind Waker
The Witcher
The Witcher 2
Valkyria Chronicles
The Last Story
There are probably a lot more that I've loved over the years.
Lately, and I don't know why, but I've started getting fixated on J-Pop and J-Rock, but only the stuff I hear and see in video games. I have a hard time getting into that music normally, but if I can associate it with something I've enjoyed in the past, I seem to have little problem listening to it. Vocal collections are big with me, stuff like Valkyrie Profile or Atelier anything, and even stuff like what Gackt did for Dirge of Cerberus.