Inigo Quilez practices some real-time cube rendering and posted the results on Vimeo. Even though this is a “rough draft”, I think it looks incredible already! Inigo says:

This is some realtime rendering experiments I made few months ago. I have always used “complex” shapes and 3d models before in my demos and never played with cubes before. This is actually a challenge for me, to make something watchable that only contains cubes. Hopefully, with the help of Simon [vimeo.com/user172715/] I will manage to do something interesting just with this cool shapes.