Nicolas strikes again with a list of interactive walls. I will just add a contribution to his ongoing work.
Creative Collision, a project by Giovanni Cannata and Anurag Sehgal, allows you to paint digital pictures by throwing rubber pebbles against an inflatable wall (I have a soft spot for anything inflatable) equipped with suitable sensors.
First, you pick up the pebble and dip it in the bowl to assign one of the three colors. You can also mix them (like yellow+red=orange).
For each color or combination you also assign to each pebble a sound
By throwing it on the fabric according to where and how strong you hit, you decide the volume and the length of the sound.