I have yet to hear a song I didn't like in a FF game. From FFX-2 the two songs that come to mind first are 1000 Words and Real Emotion. In fact, Real Emotion on a tv ad got me interested in the FF series for the first time. Music is very important for me, it can move me on many levels that are difficult to touch with only a good story and good characters and in less time then it takes for me to read a decent sized book (800+ pages in two days.) Shortly thereafter I bought a PS2 and FFX, played through FFX and got X-2 the next day.

But I am rambling now, tied for #1 on my list are 1000 Words and Real Emotion.