Heartwarming: National Lampoon's Christmas Vacation
The scene where Clark gets locked in the attic. It might not sound that heartwarming, but while he's up there, he finds old recordings of his Christmases as a child from the 1950's. It's not that hard to notice a few Manly Tears running down the side of his face.
Also, his final line. Despite the hellish disasters all December long, despite the near loss of life and sanity, in the end, he gets what he really wanted: A loving family experience at Christmas.