Not only a recreational substance for your cat, catnip has soothing medicinal properties when made into tea. It is in the mint family.
Want to learn more? Look up Catnip on Wikipedia.
STORE: In a jar on your counter. Fill a jar with cool water, stick sprigs into it, and keep out of direct sunlight. Pick off leaves that will be submerged in water. When stored this way, your herbs should keep fresh for weeks.