Limor has a great Halloween project using an Arduino and the audio shield for Arduino (Wave Shield)… She writes -
Here is a timely project for an electronic halloween pumpkin. With a bit of hacking a $1 plastic pumpkin is upgraded: a sensor embedded in the nose detects when people get close and will randomly play scary sounds and animate the LEDs on its face. The sounds are stored on an SD card so its easy to change and customize what the pumpkin says/screams, while the code is written for an Arduino so its easy to modify the behavior. I’m going to have this pumpkin outside my door to freak out the little kids who go to daycare nearby. Boo!