I've been putting together a twitter box. Shake the box and it twitters. I'm planning to put my twitter address on the side and release it as a freebie. 

The box has two small, and therefore high pitched, pipes opposing each other. Inside the box is a piston with a coin weight in the middle. Shake the box back and forth and the piston moves forcing air out of each pipe in turn. They are tuned slightly differently, the result is a satisfying warbling tweet. Twitter box!