References&Research

Arduino and sensors, similar projects (PR and Wave Shield):
Interactive chair project
This is a tumblelog about refurb-ing three old chairs. 

A foot sensitive MIDI interface by Mike Cook

Part of a large installationthat detects someone treading on a pressure sensor and transfer that information back to a computer through a MIDI interface. 

Simple Arduino Audio Samples

This tutorial explains how to do simple playback of short (~4 second), low-bitrate (8 KHz) audio samples from Arduino using only a speaker. It’s based on the PCMAudio code by Michael Smith.

Cheap and easy SD WAV player

How to build an mp3 player with Arduino.

Playing WAV files with a DAC

We're going to make a WAV player! We're going to build it with an Arduino and the AD5330 breakout board, an 8-bit DAC. 

Electronic Instrument
Step by Step Instructable to make an electronic instrument, by Amanda Ghassaei.


Arduino and sensors, tutorials & useful links:

Photoresistors 

Resistors color code
Arduino Frequency Detection 
How to access 5 buttons through 1 Arduino input
One transistor audio amplifier for Arduino Projects
Playing 1000 songs from SD card
SD Card Shield V.3.0
Soundcipher: A music sound library for Processing
Minim: audio library for people developing in the Processing environment. 
How to play WAV audio files with Arduino UNO and micro SD card
TMRpcm Arduino library for asynchronous playback of WAV files from SD card
Build a 9V battery adapter for the Arduino 
Fritzing App for drawing Arduino Schemes