Probably my power supply with 18F4320 LCD where voltage and current is controlled by digital pot (the output can be set by PC, keyboard or Potentiometer). Max 25V/5A...
My college project, It was a Programmable timer. It can be programmable from 1 ms to 99 hours and 55 mins. It had numeric keyboard, 4 seven segment displays and was made with 43 digital TTL chips.
The aim was to understand operation of almost every digital chip e.g. counters, encoders, decoders, shift registers, flip-flops and this project helped me to understand it thoroughly.
Right now, my analogue synthesiser. Has 3 oscillators, mixer, ring modulator, filter, 2 LFOs, all voltage controlled. Its pretty "messy"; By that I mean it works, but is far from perfect/ideal (ie, pitch control goes up quickly at top range).