Any shot that makes my opponent have that stunned look on his face like, "did he just do that?"
Ones I remember -
Bucharest Backhand overhead facing the back fence taking the ball on the rise after the lob got over my head and just ripping it down the alley past the stunned net man.
In a doubles match, deep in my ad court about 10-12 feet behind the baseline and about 6 feet outside the doubles sideline, whacking the ball with as much power and spin as I can muster for a short angle crosscourt winner in front of the opposing net man in their ad court. I remember thinking as I was hitting it, "There's no way I should be trying this shot."
My regular opponents have seen my full-swinging backhand passing shot taking the ball on the rise just a couple inches off the ground at the baseline and my backhand volleys a couple feet to my forehand side enough times that they are used to them.
I'm not known for playing percentage tennis.