I don't know if this would be covered by any of the above but copper grease also works a treat!
Almost all brake squeal in disc brakes comes from brake pad vibration against the caliper. To stop this the friction clips and the areas of the pad that make contact with the caliper need to be thoroughly cleaned and degreased with brake parts cleaner and lubricated with dielectric grease, caliper lube, or anti seize compound. (Any of them will work)