Another vote here for Indorex or Acclaim sprays, both work very well from experience.
As its not been mentioned you can buy a short acting treatment called capstar, its amazing stuff, and what kennels often give animals that come in with fleas. It kills every flea on the animal over a short period, but sadly doesnt last longer than 24 hours. The mass flea genocide debris it generated from one cat was unbelieveable, considering we had been using spot treatments/collars/combing and were only seeing the odd few when we did.
We did the following to eliminate an infestation we couldnt get rid of previously: Spray a small area of the house to kill any live fleas or eggs, youll want to confine the mog to this area next (we used the en-suite).
Give the capstar and lock the cat in the sprayed area for a good few hours.
While the cats locked in the area spray the rest of the house to kill anything thats left. Means all the fleas on it are now dead, and no live fleas are left in the house.
Use a spot on treatment like Advocate as you let the at out of its prison, so any eggs left on the cat cant hatch due to the spray/spot treatment.
Never had a problem since 🙂