"Always look behind the door in To Kill A Mockingbird----Robert Duvall."

His first movie role. He's also the lead in one of my favorite Outer Limits episodes.

How about Fess Parker as the Texan in the insane asylum in the movie Them or Leonard Nimoy as the soldier who reports that Parker thought he saw fly ants just before that? Nimoy also has a one liner in the Twilight Zone episode where Dean Stockwell plays the 90 day wonder 2nd Lieutenant at the end of Woirld War II who wants to kill Japanese only to find himself turned into a Japanese Lieutenant at the beginning of the war.

Or Earl Holliman as the incredibly young cook in Forbidden Planet?