1. Astaroth ~ Battle With The Fallen Angel from Shadow Hearts: Covenant. It's so... mystical and beautiful. It has bits taken from an indonesian folk song called "Seroja" and it's about a lotus, which is what Astaroth is shaped like.
2. Imbroglio from Shadow Hearts, because it's the final boss music and it sort of represents this weird mix of mysticism, epic final bosses (you are effectively up against God), and science fiction because this "God" is an alien from another planet.
3. Force your Way from Final Fantasy 8, because it's fast paced and dynamic.
4. Battle to the Death from Final Fantasy 6, because it has this whole atmosphere that mixes doom with some sort of... mysticism? I dunno. It's great.
5. Saber's Edge from Final Fantasy 13 - it is probably one of the most dynamic songs with one of the most variable key signatures I've heard in a video game.