Links

Ultrafractal                                               fantastic programm, still the reference on 2D-fractals

Hypercomplex Iterations                           more mathematical, direct from university, but take a look...

Realistic Image Synthesis Engine (RISE)    a very powerful raytracing-engine for realistic scenes (implemented in the newest fractalstudio version)

Farbrausch                                                the gods of  the demo-scene

Pouet                                                        huge collection of demos