Subblue has free Pixel Bender and Quartz Composer versions of the 3D Mandelbulb fractal, which made a splash last month.
See also Subblue's previous Pixel Benders from the last year or so: a Droste Effect filter, the Fractal Explorer, and a 4D Quaternion Julia Set Ray Tracer with added ambient occlusion.
Subblue says: "Animations can be created in Adobe After Effects using the .pbk files, but it will be very slow to render as the calculations have to be performed on the CPU rather than the GPU. The following videos were created using the QuartzComposer patch and took 15-20 minutes to render at 720x576 for about 720 frames. If only After Effects would support GPU rendering too..."