The Killing Fields when [SPOILER ALERT SPOILER ALERT SPOILER ALERT SPOILER ALERT] Sydney Schanberg and Dith Pran are reunited when they had no idea the other one was still alive.
Oh and when Willem Dafoe is killed in Platoon (It's that damn music. )
And the end of Missing (1982) when Jack Lemmon finds out what happened to his son and he's on his way back to the States. That just got me like a bayonet in the gut.