Fergo Joystick MIDI seems like a practicable software solution to getting X/Y data into a DAW.
Some people have used game pads.
Musikalisches Würfelspiel -- even Mozart wrote music by chance.
Details for DIY joystick implementation.
GIZMO is an open-source MIDI device thingy.
PACMOD MIDI DJ Controller is pretty much the thing, but it's entirely DIY Arduino.
ControllerMate is Mac OS only.
MultiControl is... something.