Cinnamon or Cayenne pepper spray??

[Izzie]

I've seen stuff in stores like lowes/home depot that deters squirrels- it's near deer and other mammal pest deterrents. No idea what it is or if it works.

Go Bitter Apple!

[Triffid]

Some Cat Deterants. (Results will vary)

Ground Black or White Pepper.
Usually very effective, just not with my freak of a cat.

Citrus.
You can get Citrus based cat deterrents or citrus smelling pot pouri around you plants to deter the cat going near.

Cat Shoo (Coleus Canina)
Used in gardens to deter invading cats, not sure if it can be potted up well as a house plants though.

Water Pistol.
Yes that old kids toy is a great training aid for cats. Just a small little hand held (not one of the soakers!) should do fine. If the cat goes near the plant you don't want it to, or start knawing at the plants just give it a quick spray and it will learn not to do that.
Just be sure not to spray it near the electrical items and such in your home. And if your cat is of the nervous variety, don't surprised if it bolts! You have been warned.

Use Sound.
The cat goes near the plant, Hiss at it or make a loud Clap. Basically telling the Cat that that's your plant, your territory and the cat should not go near, so to speak.
When Moggy moves away change you tone to that of more encouragement.