'The day the Earth stood still' is simply awsome and I like his performance. Especially his response to the Professor.
Professor Barnhardt: There must be alternatives. You must have some technology that could solve our problem.
Klaatu: Your problem is not technology. The problem is you. You lack the will to change.
Professor Barnhardt: Then help us change.
Klaatu: I cannot change your nature. You treat the world as you treat each other.
Professor Barnhardt: But every civilization reaches a crisis point eventually.
Klaatu: Most of them don't make it.
Professor Barnhardt: Yours did. How?
Klaatu: Our sun was dying. We had to evolve in order to survive.
Professor Barnhardt: So it was only when your world was threated with destruction that you became what you are now.
Professor Barnhardt: Well that's where we are. You say we're on the brink of destruction and you're right. But it's only on the brink that people find the will to change. Only at the precipice do we evolve. This is our moment. Don't take it from us, we are close to an answer.