Some spells call for herbs that are hard to find. A good source for exotic herbs is Penzeys Spices.
These are the herbs that Pendragon has in his inventory that he actually uses in spells (the attributes shown for each herb come from Scott Cunningham's Encyclopedia of Magickal Herbs):
Anise star protection, purification, youth
Bayberry bark wealth, good luck, domestic peace, fertility
Blessed (holy) thistle purification
Burdock protection, healing
Caraway seed protection, lust, health, anti-theft, mental powers
Comfrey leaf safety during travel; money
Dill protection, money, lust, love
Eyebright mental powers, psychic powers
Fennel seed protection, healing, purification
Galangal root protection, lust, health, money, psychic powers
Garlic protection, healing, lust, anti-theft
Hyssop purification, protection
Juniper berries protection, anti-theft, health
Linden flowers protection, immortality, luck, love, sleep
Mugwort strength, psychic powers, protection, prophetic dreams, healing, astral projection
Pennyroyal strength, protection, peace
Peppermint purification, sleep, healing, psychic powers
Sage immortality, longevity, wisdom, protection
Wormwood psychic powers, protection, calling spirits
Yarrow flowers courage, psychic powers