It seems that there isn't really going to be any consensus here about freezing being good or bad, but here are some alternative methods I have heard of.
Decapitation. Very quick if the fish is big enough to get a reliable grip on. Post decapitation it is necessary to somehow destroy the brain so that the head does not stay conscious in what I can only imagine as being what seams like hellish eternity, although probably only a few minutes.
Gassing. I've read that if you put the fish in a container with water and add an alka-seltzer tab or two the CO2 will knock them out and suffocate them. I'm not sure how quick and painless this is though. Doesn't alka-seltzer have lemon flavor? Would that burn the gills?
There are also instructions out there on using clove oil and alcohol. Some seem to think these are the best methods.
I always thought there must be some way to quickly do it with an electric charge, but that would bring same serious issues regarding safety into question.