Provided this is a cough from a common cold and not associated with a more serious underlying medical condition, I personally like some hot tea with a little honey or even a hot toddy. If you smoke, stop smoking.
I also use Robitussin if my cough gets bad due to bronchitis, hurting my chest and keeping me awake at night. But the most effective thing I have found is to prevent the cough in the first place by heading off an upper respiratory infection with zinc lozenges and the Neti pot. Again, this is my personal experience.
A cough is a sign of illness and could be caused by a number of things. Treatment really depends on the cause and you should get a diagnosis for any cough that lasts longer than 2-3 days or is accompanied by other symptoms such as bloody sputum, shortness of breath, chest pain or fever.