The Mandelbulb is a 3D Version of the Mandelbrot fractal. I have written my own renderer for this a little while back. I don't think the source is of much interest, as you can find better implementations around.

If that caught your interest you can find more information and pictures of the Mandelbulb on the website of Daniel White.

I played around with 2d lighting for a game I'm working on. I'll probably post how it's done once it's a bit refined (and quicker!). It's currently written in C and running on the CPU. I'm looking for a way to do it using glsl though.