Question on RGB LED Array
You can drive a 512 point array with 16 row x 32 column drivers (or vice versa). 
You can use 6 latches and 48 transistors to drive this, or use say 4 x ULN2803  (datasheet) or similar for 32 low side drive lines and 16 high side drivers. You'd still need latches or multiple ports.

ULN2803 can notionally sink 500 mA / line but total pkg dissipation reduces that. 



The MM5450 datasheet here can drive 34 LEDs. There are DIP and LCC versions. About $3.80 each from Digikey in quantity needed. 

At max clock of 500 kHz you can update it at about 10,000 times per second. It's just on/off per LED but by running at say 100 brightness levels with N cycles on and 100-N off you get 1000 frames per second.

For 8x8x8 = 512 LEDs you'd need 512 / 34 = 16 ICs. These can be daisy chained. Not the ideal solution BUT it would work. May or may not have enough segment drive current for you. Extremely easy to drive 0 just a long shift register.



132 LED driver IC !!!!

I just heard (October 2011) on PICList (thanks Colin) about this IC . 132 LED driver from Austrian Micro. Digikey sells a number of their ICs but do not list this one as yet.

They say:  


The AS1130 is a compact LED driver for 132 single LEDs. The devices can be programmed via an I²C compatible interface.

The AS1130 offers a 12x11 LED-Matrix with 1/11 cycle rate. The required lines to drive all 132 LEDs are reduced to 12 by using the cross-plexing feature optimizing space on the PCB.   

The whole LEDMatrix driving 132 LEDs can be analog dimmed from 1 to 30mA in 256 steps (8 bit). Additionally each of the 132 LEDs can be dimmed individually with 8-bit allowing 256 steps of linear dimming. 

To reduce CPU usage up to 36 frames can be stored with individual time delays between frames to play small animations automatically.

The AS1130 operates from 2.7V to 5.5V and features a very low shutdown and operational current. The device offers a programmable IRQ pin. Via a register it can be set on what event (CP request, Interface timeout, Error-detection, POR, End of Frame or End of Movie) the IRO is triggered. Also hardware scroll Function is implemented in the AS1130.

The device is available in a ultrasmall 20-pin WL-CSP and an easy to solder 28-pin SSOP package.


Product page / General details here

Data sheet here

http://www.austriamicrosystems.com/eng/led-driver/AS1130