Building a holographic mosaic
Steph and Sean Mayo built an incredible holographic mosaic of Cortana from Halo. Yes, still out of LEGO. The effect is fantastic, as seen in the video below. And even better - they wrote up some key points on how to do it yourself on MosaicBricks. This is one of the things that has to be seen in order to fully appreciate it, so click on over and watch the video.