I've watched blinken lights on my motherboard for about 2 seconds when it performed automatic overclocking. POWER, CPU, DRAM, CPU, DRAM, CPU, DRAM, TPU, BOOT. Quite entertaining.
I've seen some PC motherboards that contained integrated "POST card" in the form of bunch of LEDs or pair of 7segment displays. Sadly this seems to got replaced by few highlevel LEDs and bunch of meaningless ones, which includes stuff like backlighted PCB.
By the way many DEC Alpha boards had large amount of LEDs near the CPU (probably driven directly by the CPU) which shown state of PALcode (and thus blinked in entertaining way even when the system is up and running)
