I want something like this... have seen a couple of mods after googling a bit... but none of them mimics the actual bus traffic or memory transfers, they just do random blinking... I think it wouldn't be that hard to read memory/bus and indicate it on a LED matrix... a PCI bus analyzer maybe.
Or tap right into the various buses on the motherboard directly, dual-color LEDs for read/write on a 1024 LED array, each LED to represent a 1/10/100Kbyte block of memory. That would be awesome, to actually see the memory in realtime.