Elena, Lulu, and the AC Tifa girls were marvelous. I have a thing for Lulu, and that girl dressed up like her is GORGEOUS!!!The very first Yuna was pretty cute as well.
I should dress up as Auron. I kind of look like him (so I've been told), and even have the shades like him as well.
EDIT: Are any of those SHM (Silver Haired Men), girls? They look really feminine to me.