The Soundie (sound/hooded sweatshirt - clever, no?) is a garment "that changes its behaviour depending on how conductive you are." Made using the 'sew-in microcontroller' LilyPad Arduino and a bunch of conductive fabric, the Soundie lights up and sings different notes when you touch it.
There's an Instructables step-by-step guide, so (if you're that way inclined) you can make one yourself. Add it to the toy piano top and the electronic drum t-shirt and we're fast approaching full wearable band territory!