First published in 1983, Magical Herbalism has been the standard of magickal herbalism texts for the last ten years. It _is_ a good standard starter guide, for those of the leaves-and-fairies school of solitary Wicca.
However, the serious student of magickal herbalism should not rely on Cunningham alone. For instance, Cunningham recommends the purchase and consecration of a ritual herbal knife, of steel; most traditionalists say that herbs should be harvested with a bronze or silver knife, no steel, and kitchen witches would have something more practical -- like Chinese scissors. Many may not feel comfortable with the elaborate, fluffy rituals for dedication he uses.
The book itself covers tools the magickal herbalist should have, basics of magic (along the lines of Cunningham's _Earth, Fire, Water, Air_ and other works), and various magickal uses of herbs (protection, divination, healing, love, etc.). Cunningham describes the creation of fluid condensers, scented oils and perfumes, incenses and amulets. Herbal gardening is addressed, and chapters on magickal names of herbs, baneful herbs, and a brief witch's herbal (chapter 13) are included.
Anyone seriously interested in magickal herbalism should get a good grounding in herbs first! Any standard source on herbs is a good place to start; don't rely on Cunningham alone. Also, references to the literature on the folklore of herbs and flowers, historical herbals (such as Culpeper's), and anything else you can get your hands on can help sort out the wifty from the useful in Cunningham. On the other hand, this volume is a very nice one-volume introduction to the topic and one of the few standard works on magickal uses. Recommended for purchase and periodic re-reading.