I second anything by Rosemary Gladstar. I am slowly winnowing out books I don't often reference (I find myself doing internet searches more and more), but have kept the following herb resources:
Encyclopaedia of Herbs, Nico Vermeulen (1998) - the most complete reference I have, and most often used. Each entry includes a photograph, plant origin, name derivation, care, and how it can be used. Does not provide specific recipes.
Herbs The Healing Nature, Power Publishing (2003) - addresses 87 medicinal herbs, includes a photograph and line drawings, preparation and dosage, side effects, and history. More detailed than the above reference, but addresses fewer plants.
The Complete Book of Herbs, Lesley Brenmess (1988) - in addition to an index which includes photographs, line drawings, and uses, this also has a section for themed gardens, herbal decorations, recipes and even a section on herbal papers and other trinkets. I take this book to a comfy chair for light reading more than straight on research.
The Rodale Herb Book (1974) - this was my first herb book and will likely stay in my library forever. Good solid information, often quoting Culpeper, Gerard, Parkinson, and other herbalists in their vernacular, e.g., Gerard states that a syrup of borage 'comforteth the heart, purgeth melancholy and quieteth the phrenticke and lunaticke person.'
