Program is a tablet that causes the adult fleas to lay sterile eggs. It is very effective, but it does not kill adult fleas that usually live 2-3 months. Advantage and Frontline Top Spot are the monthly products that kill adult fleas. They are liquids that are applied to the skin at the base of the neck. They are very effective and easy to use.
Revolution is the newest product.
In addition to killing fleas, it will also prevent your cat from getting heartworms, ear mites, intestinal worms, and ticks. It is a topical that is applied once each month.