Sebastian Tomczak has documented an interesting project, where a pressure-sensitive floor has been digitised to allow creation of various sound effects with an Arduino and the original wiring system. The pressure-sensitive floor consists of several wooden triangular structures that each contain a pressure sensor whose resistance was proportional to the pressure. The system is quite retro, yet can be digitised easily as the Arduino simply measures the signal between 5V, the sensor and an analogue input - whose values are sent to a PC via serial and interpreted by MAX/MSP, and thus sounds.
Interested in sensing external sources and working with them - but not too sure where to start? Then the best way to learn is with out new Experimenter's Kit for Arduino:
The package includes a wide variety of parts, sensors and modules including: a servo motor, lights, buttons, switches, sound, sensors, breadboard, wires and more. Furthermore a Freetronics Eleven Arduino-compatible board is included to make this an extensive hobby experimenter, inventor and starter kit. However we don't leave you alone to figure it all out, included is a great project and instruction booklet, plus access to a supporting web page and software examples. In other words - this is everything you need to get started for a fun range of electronics and Arduino related projects!
So to get started or for more information and to order, check out the product page.