Notes and Volts: Build a Programmable USB Midi Controller - FADR-4
Pocket Fader
Amazon.com: AKAI Professional MIDImix - USB MIDI Controller Mixer with Assignable Faders & Master Fader, 24 Knobs and 16 Buttons, 1 to 1 Mapping With Ableton Live : Musical Instruments
Sparrow 4x100mm MIDI controller – The MIDI Maker
Softube Console 1 Fader Motorised Control Surface - Signal Sounds