For a wearable computing course I'm taking at SMU, I made a wearable input and output device for your feet: the Walkie Sockie.
The design of the Walkie Sockie is very simple. It consists of an Arduino lilypad sewed in the top of a sock with a pressure sensor by the pinkie toe:
And a vibrating motor in the arch of the foot:
Here's the source code to demonstrate the basic functionality. Upload this to an arduino with a pressure sensor on pin A5 and a vibrating motor on pin 11 and you will get immediate feedback of pressing the button. In the source code is also a ruby script and a web page to demonstrate how the walkie sockie can communicate with a computer through its serial connection.