God it's tough to choose. I'll give my picks, but they could easily change on a whim. All of these are the original versions unless noted otherwise.

FFIV:
Prelude
The Lunarians
Within the Giant

FFVI:
Terra
Cyan
Celes
Aria Di Mezzo Caeattere
New Continent
The Fierce Battle
Tina (FFVI Piano Collections)

FFVII:
Opening - Bombing Mission
Aeris
Those Chosen by the Planet

FFVIII:
Liberi Fatali

FFIX:
The Place I'll Return to Someday

FFX:
At Zanarkand

FFT:
Bland Logo
Staff Credit

Curse you Wolf Kanno for holding me to 18 tracks.