Here is a link (http://blastr.com/2010/09/best-genre-tv-episodes.php) to a pretty good list of great TV science fiction episodes. I’ve seen most of these and agree that they should be on the list. Especially Hush for Buffy, Blink for Dr. Who, and Out of Gas for Firefly (though the Firefly pilot is one of the best pilots ever, IMHO). I’m not sure the Twilight Zone episode was the best, but it was very good. I think I might have gone with Time Enough at Last (Burgess Meredeth) or To Serve Man.
What are your favorites?