cdak by Quite & Orange
Demo written in 4k and winner at the Chaos Constructions 2010 demoparty, noted recently for being used in Valve’s recent demonstration of their VR technology.
Below is an embedded video of the demo, but I must stress that the video (nor the gifs above) do not do it justice - you really should download it and watch natively on your PC. It looks stunning.
You can download the demo at Pouet here