Star Trek Episodes - My Top Ten

Over on TMP there is a thread about your favorite Star Trek Episode (original). Well who can pick just one? Here are my top ten favorite Original Star Trek Episodes:

#10  Spectre of the Gun
#9    I, Mudd
#8    Wolf in the Fold
#7    The Squire of Gothos
#6    Space Seed
#5    The Changeling
#4    Mirror, Mirror
#3    The Trouble with Tribbles
#2    A Piece of the Action
#1    The City on the Edge of Forever

Do you have your own top ten episodes? Or maybe just one.