I - Blowing up the land bridge
II - Leviathan
III - Restoring the world.
IV - Rydia returns
V - Clash on the Big Bridge. Hell, everything that happens from the landing on the second world to the fight with Gilgamesh is my favorite part of the game.
VI - Escaping the Megitek Factory
VII - When Yuffie gives the materia back and all Cloud can say is something along the lines of, "They're in the wrong spot." I can't explain why, but I love that scene.
VIII - Battle of the Gardens
IX - Battle Festival
X - Operation Mi'hen
XII - Bahamut, I know a lot people didn't like the final dungeon being that short. But I did.
XIII - The Return to Cacoon.
XIV - Godbert's introduction.

VIICC - The final battle.
X-2 - "I don't like your plan. It sucks."
XIII-2 - Pacos Amethyst and Rubrite fight