"The world's first unmanned flying desk-set," scene is, quite possibly, the most convincing instance of the Power of Friendship to ever grace a TV screen.
Not to mention the final scene, as Keating retrieves his gear after being drummed out as a dangerous radical, when his former students one by one stand on their desks and call out "O Captain, my Captain".
Starting with Todd, the quietest, timidest member, showing just how much Neil and Keating helped him.
And followed by students who weren't even in the society, including the nerdy Ill Boy and the guy who mumbled reluctantly through the 'poetry and football' scene, showing just how much impact Keating had on the class.
Mr. Keating helping Todd overcome his anxiety by having him make up a poem that impresses the entire class. "Don't you forget this" indeed.
In a deleted scene that takes place after Neil's suicide, McAllister meets with Keating, pours the both of them some tea with liquor and assures the latter it wasn't his fault.
The whole Dead Poets Society gently waking up Neil and gathering around to specifically support him after Neil's suicide.