One of our most-Tweeted posts was the recent "How to extrude light," which showed design consultancy Berg and Dentsu London's innovative use of an iPad and long-shutter photography to produce images in space.
Unsurprisingly, the technology is now available in app form for both the iPad and iPhone with Garry Sommerville's Holo-Paint--albeit currently for phrases only, so you'll not be able to draw the cool cityscape above. It allows you to select the depth, angle, color, font, and various other settings, and thus far it's ringing in at just 99 cents. (From some of the confused reviews, it's apparently not clear that you also need an SLR. You do, in order to shoot your iDevice actually extruding the word.)