NodeBox is a cool Mac OS X application that allows you to write python code and have it drawn by the application. NodeBox itself is written in python and comes with a collection of functions and libraries you can use, and even does animation (see the gallery here).
This is some really cool looking stuff. The artificial life simulations look awesome. Thanks for pointing this out. From what I can tell it uses python to generate PDF documents using Apple's display renderer. Pretty cool.
See also processing.org for an open source programming language tailored to messing with images, animation, and sound.