natural expectorant?

Does anyone know anything I could take as an expectorant? I've got a wicked summer cold kicking my butt right now and I'm managing my sinus problems with a neti pot. I have this horrible cough though and it feels like I'm trying to cough something out of my throat (not in my chest, thank goodness, or I'd be at the doctor) and I'm thinking I could help the process with an expectorant. I'm pretty sure it's just post nasal drip causing me problems. Any ideas?