I think the best natural expectorant is lemon juice. When I have excess mucus in my throat, I make myself a large glass of lemonade. The store bought stuff doesn't work though, it has to be made from fresh lemons.
I also gargle with salt water before I go to bed. It helps get rid of mucus and it also kills bacteria and relieves sore throat. I don't like taking medications unnecessarily, so I always try these remedies before I reach for over the counter drugs.