The look of Determination

This is an old Hollywood staple. Just about every big movie has one. A character usually has a lot of weight thrown down upon them, many things go wrong, and they are pushed to the brink; one final act sets them off, and sparks a fire inside, welling up their courage, anger, and willpower. Then they give it to us: The look of Determination! All we need to know is something's about to go down, and this character is about to kick some butt!!
One of my personal favorites is from The Lord Of The Rings: The Two Towers. Theoden, King of Rohan, has been under an evil spell of the White Wizard, Saruman. He is being kept under this spell by Grima Wormtongue, the King's advisor. King Theoden, this once mighty warrior, has withered away to almost nothing, barely alive and unaware of his surroundings. The great wizard Gandalf the White comes to the hall of the King and releases him from the spell. Slowly he regains his former strength. As he gazes upon his once withered hands, Gandalf says "Your fingers would remember their old strength better...if they grasped your sword.", and the King is presented with his sword. Indeed, his former strength returns to him in full, and as his eyes slowly follow the length of the blade toward the hilt, the expression in his face changes from wonder to kindled anger. He turns his eyes to Grima, who cowers and shudders at the impending wrath of the King! He is hurled out of the King's hall, down a flight of stone steps, as King Theoden follows, sword in hand, prepared to take the life of this deceitful servant of the evil Wizard Saruman.
Now that was one seriously determined look!