Licorice, Meadowsweet, Yerba dulsis, Stevia, Sweet Cicily. All can be used in minuscule quantities for a sweetener and you can grow them yourself.

Diabetics should speak to their doctors about these herbs.

Stevia is the most popular, an herb with sweet tasting leaves, 300 x sweeter than sugar, but none of the calories of sugar. The leaves are used fresh or dried.

Drying-2 or 3 fresh stevia leaves are equal to 1 tablespoon of sugar.

Finely Ground Powder- 1 teaspoon ground stevia leaf equals 1 cup sugar.

To make a Liquid Extract, steep 1 teaspoon powdered stevia leaf in 1 cup boiling water for five minutes. Cool, strain and refrigerate. 2 drops liquid equals 1 teaspoon sugar. Start with a few drops at a time to determine your personal preference. 

Too much of anything, even the 'safe' herbs, can be toxic.. Dosage and mode of use are very important things to know.
ALWAYS consult a physician or naturopath for diagnosis, confirmation and dosage recommendations before using any plant material for therapeutic or medicinal purpose.

Know The Plant - Genus AND species.
Common names vary. Know the facts about the plant.
What good is using the leaves in tea if the only good use of the plant is the powdering of the root? And what if the leaves in that new pot of tea are toxic, but the roots are not?

If you have children, Make sure the plants in your garden are kid safe. Educate them not to eat from the garden unless you are with them. Know what plants are safe for your pets as well.

Ideally, grow it yourself. That way you'll know the plant and how it was grown. Plus, you're not supporting (in some herbal products) the endangerment of plants in the wild.

Don't Wild Gather!
Unless you are an expert at identifying and have permission to do so. Within each genus there's good plants and look alikes that can do great harm.

Wild gathering is also a threat to our native plants and habitats. Both by reducing the plant population in the wild and by the damage we do to habitat by tromping around in sensitive soil cultures.