Aawww, s**t, I've got so many favourites. I'll list them here:
Aeris' Theme (why didn't you list that?)
Battle Theme, aka Fighting, or Those Who Fight.
Boss Battle Theme, aka Still More Fighting, or Those Who Fight Further
Cid's Theme
The Highwind Takes To The Skies (Airship theme)
J-E-N-O-V-A (God, I love this)
Birth of God (Bizarro Sephiroth's Boss Battle)
One Winged Angel (Of course)
However, I also love the music mixes in "Advent Children", particularly the two versions of "Fighting" (called "Tataku Mono Tachi" in Japanese, with a piano version from the FF7 Piano tracks over Tifa's fight with Loz, and a new hard rock version over Reno and Rude's fight with Loz and Yazoo), the version of "J-E-N-O-V-A" over Cloud and Kadaj's fight, and, in particular, the new version of "One-Winged Angel". Hard rock and orchestra go surprisingly well in this song, and the lyrics (Once you translate them from Latin) make a lot more sense in the context.
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(No longer a mod)
On sabbatical...