My personal favorite is still "The Invaders", featuring a true virtuoso performance by Agnes Moorehead. She is the only member of the cast, and has not a single line of dialogue in the entire twenty-five minute episode. If you have never seen it (or even if you have), this is a can't miss view the next time it airs.
that a favourite of mine
and of course the classic, "The Monsters Are Due on Maple Street"
"Maple Street, U.S.A. Late summer. A tree-lined little world of front porch gliders, barbecues, the laughter of children, and the bell of an ice-cream vendor. At the sound of the roar and the flash of light, it will be precisely 6:43pm on Maple Street. This is Maple Street on a late Saturday afternoon. Maple Street, in the last calm and reflective moment before the monsters came."
"The tools of conquest do not necessarily come with bombs and explosions and fallout. There are weapons that are simply thoughts... attitudes... prejudices. To be found only in the minds of men. For the record, prejudices can kill, and suspicion can destroy, and the thoughtless, frightened search for a scapegoat has a fallout all of its own for the children, and the children yet unborn. And the pity of it is... that these things cannot be confined to... The Twilight Zone."
MSNBC correspondent Keith Olbermann cited this episode as an allegory for the Bush Administration's conduct of the War on Terror in a "Special Comment" aired on the fifth anniversary of the September 11th attacks, titled "This hole in the ground."