I want to second the recommendation for Impromptu as well:
- Wholesale utilization of your Mac: audio units, camera, openGL...etc (I actually ended up buying a Mac after playing around with this app.)
- Very simple and easy to start : The tutorial gets to the fun fast. Perhaps the clumsiest aspect is getting the keybindings installed : (you will need to install in ~/Library/KeyBindings/DefaultKeyBinding.dict)
- It uses Scheme(Lisp dialect) a highly iterative language, suitable for prototyping apps one line at a time.
