http://i30www.ira.uk.de/~ukrueger/fractals/
This site takes you on a journey into the depth of a Mandelbrot set. Click on a location within the fractal and zoom in on the details of that location. For the theoretically inclined there is an essay on the theory behind the Mandelbrot set. If you can't get enough fractals then select the database and surf through 500 images.