+1 on the Zicam, but for me, it only works if I get on it as soon as I feel like I'm even trying to catch a cold. If I get on the Zicam early enough, I might be able to avoid the cold entirely. I always make sure to have a couple of swabs stashed in my purse, medicine cabinet and travel kit year round, so if I start to catch a cold I can get on the Zicam immediately.

They're not 100% sure how it works (like most pharmaceuticals including prescription ones fwiw), but one of the theories is that the zinc prevents the viruses from settling on the tissues. So I actually alternate the nasal swabs with the rapid-melt lozenges, to get it in my nose and throat both.