This project uses the microphone on your PC to move the sprite. The louder you clap, the higher the character goes. One unexpected bonus is that it also responds to music playing on my computer, so you could use this as the basis of a music visualiser.
This is an example from the 2nd Edition of the book Scratch Programming in Easy Steps by Sean McManus. More info here: http://www.sean.co.uk/books/scratch-programming-in-easy-steps/index.shtm
