The Little Mermaid - Part Of Your World (Reprise)... She is leaning on the rock and looking at the guy on the beach. She sings the main refrain and as she hits the word 'World' in the line "part of your..... world" the waves crash around her and the music swells.
The Passion of the Christ - When Jesus is walking through the streets with his cross and he stumbles and falls. Mary has a flashback to when he falls as a child and she scoops him up and kisses him better. Then it cuts back to his bloodied, broken face and there's nothing she can do to take the pain away.
It's A Wonderful Life - Just the whole idea of seeing how life would be different for others if you weren't around.
Wall.E - The emotion portrayed between two inanimate, non-speaking characters is amazing.
Platoon - That damn Adagio for Strings!!! "Barnes! BARNES!!!"
Toy Story 2 - Jesse's Song. Agreed with all who have mentioned this.
AntiChrist - The begining scene. The sex bit is great but then it moves onto the child. You realise what is going to happen but don't expect it to be so visceral! As a father, that made me cry and cringe all at the same time.