So you probably noticed that hooking up the potentiometer and the photoresistor was very similar. This is because both kinds of sensors are what are called resistive sensors. There are dozens of different kinds of resistive sensors that you should be able to hook up to your MIDI controller using what you know including: IR distance sensors, motion sensors, stretch and bend sensors, force sensors, accelerometers (motion, tilt and slope measurement), magnetic sensors, temperature sensors and more.

Locally (Victoria, BC)

QUEALE ELECTRONICS
2017A GOVERNMENT STREET
VICTORIA, BC V8T 4N9
TEL: 250-388-6111
FAX: 250-386-9151

Queale electronics carries a variety of switches, potentiometers, and photoresistors. They also carry a lot of general electronics supplies and tools e.g. hookup wire, breadboards, wire strippers etc.

Online (Canadian Distributors)

Robotshop Robotshop is a very user freindly place to find sensors. You can also buy Arduinos and Arduino accessories here.

Digikey is a cheap place to source parts but it can be an intimidating site for beginners. There are literally thousands of each kind of component so it can be difficult to find what you are looking for. Prices include duty and Canadian taxes and orders ship incredibly fast i.e usually at your door within 24 hours.