Up until the last 10 minutes, a Wonderful Life may be the saddest movie ever made. The druggist son dies and takes it out on George's bad ear; his father dies and he chooses the building and loan over college; his brother comes home married with a job offer, and he realizes his dreams are over ( the look on Stewart's face is heartbreaking); the economy collapses on his wedding day and he hands over his honeymoon money to the town to keep the building and loan afloat; etc., etc. The saddest scene is when George explodes on the family, yelling at his kids then destroying the corner of the room where he was keeping just a small part of his big dreams alive. When he turns to face his family... Wow. James Stewart was one hell of an actor. The scene in the bar when he is praying is incredible, too.
If you're not crying by the end of the movie when he opens the book and reads the message from Clarence, then you don't have a pulse.