From Dr. Pitcairn's Complete Guide to Natural Health for Dogs and Cats:
"Combine one part of as many of each of these powdered herbs as you can find: eucalyptus, rosemary, fennel, yellow dock, wormwood and rue. Put these herbs in a shaker top jar, such as a jar used for parsley flakes.
Apply the flea powder sparingly to your pet's coat by brushing backward with your hand or the comb and sprinkling it into the base of the hairs, especially on the neck, back and belly. To combat severe infestations, use several times a week. Afterward, put your pet outside for a while so the fleas vacate in the yard and not in your house. "
I'm pretty sure most health food stores sell herbal flea powders too if you don't want to make your own.
Or try making a skin tonic:
"Thinly slice a lemon, including the peel. Add it to 1 pint of near boiling water and let it steep overnight. The next day, sponge the solution onto the animal's skin and let it dry. You can use this daily for sever problems involving fleas. "
You can also get flea collars with natural oils in them. some are made so that you can "reload" them when the oil gets used up. I've never used one of those on my dog so I can't really tell you if it works or not.
I hope that helps. fleas are a pain.