I have been meaning to try out Processing (a.k.a. Proce55ing) for ages, now. Processing is a Java-like language which includes a simple development environment which makes generating graphics, animation, and sound simple. You can see some impressive examples at the Processing site's exhibition page.
I played with Processing for the past week or so, and my first non-trivial "sketch" is a modification of the Penrose Tile example written by Geraldine Sarmiento included with Processing. It is an algorithmically-generated plantlike form. The iterative method used is called an L-System, introduced by the botanist Aristid Lindenmayer (hence the "L").
Back in the 80s, when fractals, cellular automata, and other iterative and recursive things were the rage, this beautiful book (which I have a copy of) was produced: The Algorithmic Beauty of Plants, by Przemyslaw Prusinkiewicz and Aristid Lindenmayer. It is out of print, but you can download a full high-resolution copy at that link, which also lists correction.