Evidence suggests zinc gluconate and zinc acetate shortens colds by about a day. As far as I know, zinc is the only cold remedy with good evidence for it. Cochrane Reviews, famous for their quality, has a review of the evidence for it, which is strong, but not perfect.
How to find it? Look
for dissolvable zinc tablets at the pharmacy that say they’re for colds. They will often say they are ‘homeopathic’ because this allows them to skirt FDA regulations. Don’t let that scare you off.
Make sure to follow the directions on the back, you want to avoid eating or drinking for 15 minutes after as its thought to work by coating the back of your throat with zinc ions. Also, start using them as soon as you notice symptoms.
Hymn to Reason 