Onions and Garlic
Onions and garlic have been highly regarded for medicinal and culinary purposes for millenia. As medicine, they've been used to treat many complaints such as balding, asthma, burns, insect bites, and to promote longevity. As food they've been used in everything from soup to dessert. Because they are so versatile and easy to grow, you should have some in your garden. In my opinion, you can never have enough onions.
To learn more, read our article, Never Enough Onions.