Fresh ginger rhizome.
Ginger root is used in a number of teas and tisanes - such as Lemon and Ginger (which is produced by various companies), and several of the teas produced by Dalgety. Recipes for preparing ginger tea can be readily found on the web.
There are said to be negative effects from drinking too much ginger tea.
For a more comprehensive treatment, see the article on 
Wikipedia.