Great question!
I think the best thing a mother can teach a son is how a wife should treat her husband so that when he is looking for a wife he looks for someone that will treat him well. This is done through example and is why it's so important to have a good strong traditional marriage.

Also I see you remembered your password :)

Critical thinking, that difficult problems can be overcome with hard work and discipline, emotional control.

Edit: I guess what I'm missing is something to stop them becoming a sociopathic monster: perhaps empathy and the value of human relationships.

That nothing comes for free. No allowance, every dollar he should earn. I think this applies for daughters as well.