I have a few lines, I really liked

From the English Version:
''Shut ya gob, lassie!'' - Cait Sith (I'm sure he says it on the Airship towards the final battle)
''Spikey!'' - Barret (When you first hear his voice, he calls Cloud 'Spikey' when he says bye)

From the Japanese Version:
''Rude, you look awesome!'' - Reno (When at the Healing Lodge)
''You're late, Bitch!'' - Barret (when facing Bahamut Sin)
''I want to be forgiven...'' - Cloud (He sounds cool when he says it!)

Thats all I can think of now..