Possible? Plug in Sensors?

I want to build a basic MIDI controller using an Arduino, just a button and potentiometers, but I want it to be expandable. So, on the outside case of my little controller would it be possible to have some kind of inputs that would be wired to the Arduino, that I can plug other sensors into?

Maybe I could connect one Arduino with one set of sensors to the base Arduino?

I honestly dont really know what Im talking about, and what I said will probably need clarification, Im gonna try to do some sketches, thank you.

Depends on how you define 'sensor' and what kind you need.
if it will just be buttons or potentiometers, cetainly.

Yeah, groups of potentiometers and buttons that I could plug into the main board. Im drawing up a sketch.

So after a bit of research, could I have an XBee unit thingy on the main module, and multiple slave XBee's with potentiometers and what not that connect to the main?
And as I understand it the slave XBee's can take in data from potentiometers and what not on their own, without an Arduino?

Well one method you could consider is using a shield designed to have external sensors and componets plugged into it.
Here they cover the whole product line:

http://www.seeedstudio.com/depot/images/product/Electronic%20Bricks%20Vol1.1.pdf

Here is the 'mother shield' board:

http://www.seeedstudio.com/depot/electronic-brick-shield-v4-p-458.html?cPath=48_49&zenid=9f6118c193cee9f8b7337d4df91a2eca

and using cables like these:

http://www.seeedstudio.com/depot/electronic-brick-fully-buckled-3-wire-cable-p-485.html?cPath=48_57&zenid=9f6118c193cee9f8b7337d4df91a2eca

You can plug in external components like:

http://www.seeedstudio.com/depot/electronic-brick-light-sensoranalog-p-474.html?cPath=48_52&zenid=9f6118c193cee9f8b7337d4df91a2eca

http://www.seeedstudio.com/depot/electronic-brick-adkey-module-p-500.html?cPath=48_50&zenid=9f6118c193cee9f8b7337d4df91a2eca

http://www.seeedstudio.com/depot/electronic-brick-real-time-clock-moduleds1307-p-491.html?cPath=48_59&zenid=9f6118c193cee9f8b7337d4df91a2eca

http://www.seeedstudio.com/depot/electronic-brick-5v-relay-module-digital-p-479.html?cPath=48_53&zenid=9f6118c193cee9f8b7337d4df91a2eca

http://www.seeedstudio.com/depot/electronic-brick-playstation2-analog-joystickanalog-p-468.html?cPath=48_50&zenid=9f6118c193cee9f8b7337d4df91a2eca

Lefty

Ahh this is great stuff, thank you!