Yeah, that is classic along, of course, with: "Leave the gun. Take the canoli's." Can you imagine writing that line -- the guy had to know immediately that it would be a classic.
For acting though, my favorites are two related, non-verbal Pacino scenes. I really don't care for his acting over the last 20 years but he is absolutely brilliant with his face in the scenes where he: 1) makes his decision to go to the dark side in the meeting with Sonny after the cop breaks his jaw; and 2) the scene in the Cuban nightclub when he realizes Fredo betrayed him. Now THAT'S acting.........