IO2Technology has an interesting free-space display called Heliodisplay. The image floats in mid-air above the display unit, doesn't require glasses to view it, and can even be touched. The image is projected in two dimensional space, but supposedly the images appear to be three dimensional when viewed from more than a few feet away. The videos available on the web site seem to corroborate this statement.
The Heliodisplay technology is patent pending so IO2's web site doesn't contain much technical information. The displayed images are up to 22" diagonal and all the video sources you'd expect are supported. Touching the image provides no physical feedback, but a finger can be used as cursor, turning the Heliodisplay into a virtual touchscreen.