Great answers! Since I have so many herbs growing in and about my garden. Garlic as the king of herbal medicine, echinacea, valerian, heal-all,all kinds of mints, elecampane for coughs/lungs, scullcap, motherwort, lemon balm, oregano, thyme, comfrey, cayenne, lobelia, etc. My focus on this question was those that I can't grow but would really miss if I didn't have. Peppercorn is a great one suggested that I didn't get. But my five are:
1. Turmeric - a great anti-inflammatory, second only to garlic in my book, great for cooking indian food (yum)
2. Ginger - great digestive, stimulates circulation
3. Cinnamon - good for so many things - triples the effectiveness of insulin in diabetics, digestive and tastes well, like cinnamon
4. Vanilla - not especially known for its medicinal properties, but baking and cooking desserts without it is just not right
5. Cacao - life without chocolate would just be sad
I've got a nice stock pile of each of these. I'm an ardent believer in food as medicine.