This may be the coolest DIY MIDI controller yet.
Markus Berger built this life-size MIDI organ controller for Native Instruments B4 virtual instrument:
The goal of this project was to build a MIDI Organ Controller to play and control the Native Instruments B4 (II) virtual organ software. Just like the software this project attempts to replicate the ‘real thing’—the classic Hammond B3—as much as possible. All of the software’s functionality known from the original instrument can be controlled from this controller. There is no need to take a look at the computer display or to control the software with the mouse or computer keyboard at any time.