If you like synthesizers AND Lego, this is a real curiosity.  Teenage Engineering, creatos of the modern OP-1 synth, offers a Lego-compatible accessory, the "brick shaft" knob:

Each can be affixed to the color-coded buttons of an OP-1 synth, and you use your Lego colletion to add gears, cranks, etc. to your buttons.  Heck, I can imagine those geniuses who use Mindstorms to make a robot that live-tweaks the controls as perfoms its own  compisitions.