According to About.com, the best commercial indoor cat repellent is Mutivet's Ssscat! cat repellent training system. The system is often used to deter cats from jumping on counters, messing with plants and going into off-limit areas of the house.
The Ssscat! System sounds off an alarm and emits an odorless spray when cats get too close. Other repellents such as double-sided tape and bitter apple spray are also effective cat deterrents. According to The Nest, natural repellents such as nontoxic essential oils can be placed in off-limit areas. Spraying cats with water from a water bottle is another effective way to keep cats out of certain areas.