Exactly how we interact with our music creation greatly effects what sort of music we will make, and how it will sound. New instruments and interfaces for music control have been one of the main motivators for innovation in the field. Just think of what the whammy bar or the theremin did for the types of sounds people made.
This page will cover the fundamental principles behind many of the currently existing input devices. Once you know how something works, you can then bend it to your needs.
and more in the works:
Light dependent resistors (LDRs or CDS photocells)
Piezo films and ceramic discs