I\'ve looked through a number of other S.O. questions, followed all of the advice, but I\'m still clueless as to why I can\'t get shadows to render on this very basic scene.
You need to set
cube.castShadow = true;
and make sure the shadow camera far plane reaches the cube.
Fiddle: http://jsfiddle.net/4Txgp/13/
three.js r.58