Fractals and 3D are an interesting problem: http://www.skytopia.com/project/fractal/mandelbulb.html

That page is older, but based on the performance at the time I'm still not sure you could render them in sufficient real-time to make VR a useful thing.

(I leap to the assumption you're referring to 3D fractals because merely adding VR to a 2D fractal viewer does not seem like a useful thing to do.)