Vinegar is excellent for keeping bugs under control and is 100% non-toxic to you and your cat.
Whip up a simple mixture of apple vinegar and water. If your feline will let you, you can apply the mixture with a spray bottle, but most cats won't like this method at all. The easiest way is the wet your cat's brush in the solution and then brush them with it.
Pay special attention to their back and behind their ears. Within no time, you'll start to notice the results. Vinegar also helps keep hair shinier, so in addition to being flea-free your cat's fur will also be glowing!