Man, when 'Otherworld' first played at the Zanarkand stadium I nearly lost my s**t (in a good way, mind you) the first time I saw it. Now, I own Nobuo Uematsu's selection of the OST for FFX (the single disc as opposed to the full 91-track four-disc set). I love every track from that OST.
I need to get the others too. Particularly VII. VIII, IX. I love the reactor theme.