It's cold season here and there's a pretty good roundup of cold treatments in a recent article on Science-Based Medicine:
Treating The Common Cold
Basically, the author concludes the best tactic is to tough it out with maybe mitigation of symptoms with antihistamines and decongestants. I personally think supplements may be a harmless placebo (except zinc nasal sprays) to avoid the drugs. I got no jip with that (well...) but people should be well-informed.
(related: Coughs, colds, and the “appealing but mistaken concept of boosting the immune system)