I guess it would depend on what you wanted to do with the herbs.

The first basic book I would recommend is 'The Herb Book' by John Lust.

If you want to work with herbal preperation (tictures, infusions etc) then 'The Herbal Medicine Maker's Handbook: A Home Manual'

If you are looking for magickal properties then I would look at the Scot Cunningham book on Herbs.

If you want an over view on how and why herbs were used then I would recommend 'Healing Traditions & Spiritual Practices of Wicca'by Debbie Michaud who is also known as GreyWing from her website The Manorhouse for Wiccan Studies' which has been online for many many years.
http://www.geocities.com/athens/4177/

All are still available at Amazon.com I believe.
Namaste
Silver

Rosemary Gladstar's Family Herbal is a great sourcebook.