Recently, I buy a 3D Led cube from mainland China, it contains 8x8x8 Blue Leds. It powers up by normal USB +5V source. Also, It comes with a pre-programmed MCU, you get few features build-in (looping some cool 3d patterns, lamp and audio visualizer) .
The audio visualizer is very cool and handy, you can just plug in an audio jack and play music. There is API for you to control the leds via i2c, but I don't have time to try.
Let's see some photos: