Is the frequency of light restricted? What are the factors that limit the frequency of light?  Can it have wavelengths ranging between zero and infinity?
 A: The electromagnetic spectrum does range between (almost) zero and (almost) infinity. It's just that your eyes are sensitive to a very small part of it (from about 380 nm to about 800 nm).
At the lowest frequencies, it becomes difficult to recognize the signal from background fluctuations.
From this site: "Gamma-rays are detected by observing the effects they have on matter." So the upper end of the EM spectrum is probably above 300 EHz, but there are no EM generators at those frequencies.
A: Theoretically, the shortest wavelengths of light would be limited by the Planck length, at some point the space 'closed' by the wavelength would be so small that gravitational effects would dominate, in the same way that black holes can bend light passing near their event horizon at very small scales the wavelength would be so small that it might be at the centre of its own super-tiny black hole and so be unable to escape. 
We don't have much of an understanding of what happens at these scales of space though, the Planck length is 10-20 times smaller than the diameter of a proton and what gravity does at this extreme is one of physics' central mysteries.       
I'm not too sure about what the limits of the lowest frequency / longest wavelength are, I suppose that the longest wavelength would be limited by the age and size of the universe, as far as we know the Universe has an age and the speed of light has a fixed upper limit so perhaps the longest possible wavelength is linked somehow to whether the Universe is expanding or not and whether the big bang really was the start of all quantum events.    
A: Do keep in mind that the frequency of light is reference frame dependent.  So, for example, the cosmic background microwave radiation would appear as a concentrated gamma radiation source 'in front' to an observer with ultra-relativistic speed relative to the CMB.
In other words, light emitted from a body of a particular frequency in that body's frame of reference, could have arbitrarily low or arbitrarily high frequency in relatively moving reference frames.
A: The lowest frequency limit is provided by the size of the universe. If we could make an antenna that size, the frequency would be "very close" to zero. The highest EM frequency limit is provided by the smallest antenna we could make. I believe that would be the size of a hydrogen atom, giving us, $$F_u = \frac{2.997x10^8}{6.28x5.29x$10^{-11}} = 9.02x10^{17}Hz$$
Note: These are theoretical limits, the current "real" limits are as reported on Wikipedia. 
