One unique use of essential oils is in combination with astrology. Here's a brief summary from Aromatherapy for Healing the Spirit:
Sun: Source of light and life; linked to the heart and circulatory system. Essential oils: rosemary, laurel, and frankincense.
Moon: Reflects yin energy; linked to digestion and nourishment, pancreas, and mammary glands. Essential oils: jasmine, coriander, and clary sage.
Mercury: Related to the nervous system, thyroid gland, and speech and hearing. Essential oils: fennel and caraway.
Venus: Pertains to the skin, parathyroid gland, and female reproductive system. Essential oils: rose, geranium, lemon, and benzoin.
Mars: Reflected in blood, muscles, adrenal glands, and male reproductive system. Essential oils: ginger, juniper, and other pungent essential oils.
Jupiter: Represents bodily growth, liver, and anterior pituitary gland. Essential oils: Hyssop and orange.
Saturn: Governs bones, posterior pituitary gland, and aging process. Essential oil: cedarwood.
Here are more resources about astrology and essential oils:
Aromatherapy and Astrology at AromaWeb
Series of articles covering each astrological sign by Suzanne Bovenizer
Book: Astrological Aromatherapy by Patricia Davis
And a cool infographic from Bulk Apothecary: