I've discovered Processing (www.processing.org) a few months back and it's been my new favorite toy.

"Processing is an open source programming language and environment for people who want to program images, animation, and interactions. It is used by students, artists, designers, researchers, and hobbyists for learning, prototyping, and production."

I've been working on a few projects involving image processing, real-time video distortion, fluid dynamics and a whole lot of basic vector math.

Here's a small screen capture of the latest thing I've been working on: