Return of the Jedi
This is probably the first thing most sci-fi fans think of when the whole father-son thing comes up, and with good reason; Luke and Anakin's complicated familial relationship is one for the ages. After finally finding out who his father really is in Empire, Luke tries to convince dad to shun the Dark Side, despite all evidence that he's way, way too late. Of course, this leads to the chill-inducing scene in which Vader, faced with the destruction of his offpsring, makes a galaxy-altering decision. If you don't want to hug it out with your dad after watching this, we don't know what to say.