marian42:
I would use two 595s. They use one clock and one latch pin and two data pins and they will receive data simultaneously.
Thats exactly how I did it.
http://arduino.cc/forum/index.php/topic,123495.0.html
My first 4x4x4 cube was 4 220 ohm resisters, 64 LEDs (white LEDs from 4.5v flashlights) It has 4 planes (resistered connected to the anodes)of 16 LEDs. I later changed it to using 2 74HC595 (16 bit) to control the cathodes.