I like:
Shuffle Or Boogie (FFVII)
JENOVA COMPLETE(FFVII)
Liberi Fatali(FFVIII)
The Oath(FFVIII)
Something to protect(FFIX)
Wicked Melody(FFIX)
Fithos Lusec Wecos Vinosec(FFVIII)

and of course, my favorite: Otherworld(FFX)

What are yours?