I noticed this linked from both Atom and Real-time Rendering blogs. Cyril Crassin, the guy behind the amazing gigavoxels raytracing, has got a 3d Mandelbrot fractal rendering in real time.
As we know there isn't actually a 3rd dimension to the imaginary plane so some manipulation is required. The chap who discovered a good way of transforming it to 3d ( the Mandelbulb ) has a website which you can find here. Well worth reading and some pretty amazing images!
As a side note: I've owned the book: "Real-time Rendering" for a number of years now and it is an invaluable resource. The Real-time Rendering blog mentioned above is the blog by the authors of the book.