Need to add audio to your ATmega238 based Arduino? Check out Adafruit Wave Shield – a low cost easy-to-make kit that can play up to 22KHz 12 bit uncompress audio files of any length. It features onboard DAC, filter and op-amp for high quality output. Audio files are fed from SD/MMC card and volume can be controlled with onboard thumbwheel potentiometer.
Using the Arduino library for this shield, play audio when buttons are pressed or when a switch/sensor goes off, or when serial data is received and so on.
Buy Adafruit Wave Shield for Arduino from Pakronics:
Adafruit Wave Shield for Arduino Kit