Mr. Keating dealing with Todd's insecurity. First, Keating pushes the kid to let out a barbaric "Yawp!" and has him turn in place imagining images and action until he find himself spontaneously creating a terrific poem on the spot as he is swept along by his creative spirit, stunning his class and himself. Especially when Keating leans in close and says "Don't you forget this."
The end scene, where most of the boys literally jump on desks shouting "Oh captain, my captain!" in defiance to the school's tyranny. This includes Todd being the first one to do so and Robin William's line "Thank you, boys."
Knox should get a special mention since he was the first to do so after Todd. He could have easily left Todd to stand by himself and suffer from Nolan's wrath by himself, but instead decided to stand alongside him in support of both him and Keating, spurring the other students to do the same.
The moment during the desk-standing, when Hopkins stood on his desk, because he'd been the most resistant in the class all along.
The "unmanned flying desk set" scene goes from a tear-jerking scene, with Todd looking like he's about to cry, telling Neil it's his birthday and his parents sent him the same thing they did the previous year, to at once funny, heartwarming and awesome as Neil points out that the shape is very aerodynamic, and they throw it off the top of the school. Especially Neil's follow-up comment: "Don't worry. You'll get another one next year."
"Damn it Neil. The name's Nuwanda." Proving that despite his recklessness and frequent arrogance, Charlie is actually very loyal to his friends and isn't about to rat them out to save his reputation.
Charlie gets another one when he punches Cameron, who had turned on both the society and Mr Keating in order to stay on the school's good side and save himself. Despite the subsequent reminder that doing so probably destroyed all Charlie's chances of not getting expelled, it was still incredibly satisfying.