My favorite would be the Rock-The-Cradle. It's just soooo sweet and soooo smooth.
Although I would like to see that dunk Andrew said, would be very interesting to see... (Only seen MJ do a windmill once).
As far as the lay-up goes, I would say it would be the play against the Nets when he went up in the air, faked the ball one way, brought it back, faked another way, then brought it back again and then finished by laying it up on the other side of the hoop...