This was one of the more impressive exhibits at SIGGRAPH. It was a very simple display, but it was 3D and it floated in the air. You could walk around the display and see it from any angle. In the video clip, you can hear the buzz from the electricity...it sounded like at any moment lightning bolts were going to shoot out and fry us all, a la Raiders of the Lost Ark.
Here's a link to more information about how this "True 3D Display Using Laser Plasma in the Air" really works from the people that did it.