Effect:
You show the upper card in the deck. Cut the deck and the card is still on top.

Method:
When you cut the deck, flip the upper half to a 45 degree angle.
Grab the upper card with your fingers and drag the upper half of the deck away from the card.
Then put it under the other. The card is then on the top.
The funny thing is when you show that the deck is normal, with 52 different cards.
You can repeat this trick.