The Chariot race between Judah and Messala. Expertly staged with every edit, every stunt, every close-up detailing the hatred and bloodlust the two characters have against each other. Still considered the greatest action sequence in film history.
A more low-key example would be the scene where Judah and Messala toss spears at a rafter beam and nail it.
Judah's dramatic boast, "I told you I would return," and his demanding of Messala to find his family or else. This man has just come back from a certifiable death sentence - he shouldn't have even survived the trek to the boat! - so if he swears vengeance on you, not even the whole Roman Empire can help you (especially when he comes back the favored son of a Roman superior).
The 'Miracle' sequence, right after Christ's death on the cross: A thunderstorm erupts, forcing Judah's leprosy-stricken sister and mother to seek shelter in a cave. Amidst torrential rain and repeated lightening strikes, they suddenly realize their affliction has disappeared. As the music swells, CUT TO montage of Christ's blood flowing to the base of the cross and being carried overland by rain-swollen streams, symbolically cleansing the world.
Jesus giving Judah the water. There's a Roman soldier yelling at him to stop, and he keeps pouring it for Judah without so much as flinching. When the soldier gets angry and steps forward, he stands up tall and looks the man in the eye. The man goes from anger to confusion to sheepishness, then backs off.
Judah's escape from the warship, freeing many other slaves in the process, saving Quintus Arrius' life with his spear-throwing skills and shoving a torch in the face of an enemy soldier.