Inside the house SALT is my flea cure.
We had a cat that brought fleas into the house when we had two babies at the time. I was VERY afraid of spraying anything and did my research.
Salt kills the larva of the flea much like salting a slug on a microscopic level. It works its way down into the carpet pad, furniture cracks and even

the cracks of my old hardwood floors. (Yes I know... I am evil). You just use plain cheap salt with no iodine and race through the house like the sandman. When first applied leave it as long as you can possibly stand it walking it into the carpets and brooming it all around. (24 hours +) Then vacuum well and reapply as needed.
Once the salt is worked down into all of the cracks it just stays there working for years.
Plus sides:
CHEAP
Actually works
Totally safe
Problems:
Awful to deal with for that first treatment time - it gets everywhere.
Tends to draw humidity out of the air and leave the floors damp
Could damage your floor, but most carpets are synthetic and it should not matter.
Can NOT be used outside. It will kill plants and make soil sterile for years.
It was and IS WAY worth it to me