The SynPad is a position sensitive midi drum pad that you can build yourself using simple materials and tools for around 50 UK pounds (depending on what materials you already have, and how many pads you want to make.) The idea is to produce a pad which can detect where on the pad you have hit it as well as how hard, so that the synth it is driving can change the sound continuously according to the x and y coordinates of the strike.

DO IT YOURSELF.