Konstruct might be the app for you. Not only does the iPhone app let you produce generative art using words, warbles and whistles, but it also uses augmented reality to bring your artistic creation to life.
To get started, you first need to print out the Konstruct marker and place it wherever you'd like to create your AR sculpture -- it could be on your living room wall, or on the floor of your bathroom, it doesn't matter. Open the app, point your iPhone at the marker, and start making some noises! Once you're done, you can save your creation, or simply wipe the slate clean and start again.
The volume of your voice affects the size of the shapes that are drawn on the screen, and you can move your head around to alter the path of your 'brush' -- but to change the shape of your brush or modify the color palette you have to use a menu. Without knowledge of the app's internal workings, it's hard to say what the actual difference between whistling, talking and singing is -- and judging by the developer's affinity for whistling in the demo video (after the break), the app probably doesn't perform that much analysis on your input.
Still, Konstruct is just a prototype! A later version could do away with menus and rely entirely on the location, tonality, quality and amplitude of your voice -- and judging by the the words of the developer, James Alliban, there is definitely more in store for Konstruct: "The idea of transforming entire cities into user generated virtual art galleries really appeals to me. I see Konstruct as an early prototype that will hopefully be realised in this form in the future."
Download Konstruct for free from the App Store (iPhone 3GS and 4 only)
[Thanks to Richard for the tip!]