What are the lowest authorized minimums for each ILS category?
As Carlo mentioned in the comments, the minimums may vary from place to place to place. Here in the US you can find all that information here. Or you can buy a printed copy from a variety of aviation suppliers. 

This order published in 2012 sets some minimum performance guide lines for minimums as well. For example, 


  (2) The following is the minimum class of performance (refer to
  Appendix B) required for an ILS to support a published Title 14 of the
  Code of Federal Regulations (14 CFR) part 97 CAT II or III SIAP: 
  
  
  Class II/T/2 for operations not less than RVR 1200. 
  Class II/D/2
  for operations not less than RVR 1000. 
  Class III/D/3 for
  operations not less than RVR 700. 
  Class III/E/3 for operations not
  less than RVR 600. 
  Class III/E/4 for operations less than RVR 600.
  


See appendix B in that order for more information. 

This may also be of some interest.