When the first symptoms of a cold hit me, I always reach for the vitamin C. I take about 1 gram every hour. You know when you're at full capacity because the bowels loosen. At that point, drop the dosing back. This works for me.
If I am too late to catch the beginnings of the cold, I find aromatherapy oils are fantastic. There are various effective against colds, but eucalyptus, camphor and methol are good places to start. You can use one or a blend of several, add them to steaming bowls of water to inhale, or sniff them straight from the bottle. You could also dilute them with oil or alcohol to make a rub to apply to your skin or mix to add to your bath. These oils are the main active ingredients in the Vicks vapour rub. The pure oils are more versatile, although the Vicks is less bother. If you go down the path of buying the oils and diluting them in alcohol or oil, you can find appropriate ratios on internet sites. You can't put these oils straight onto the skin without diluting them.
To ward off colds and germs, I use a blend of cinnamon, pine and orange aromatherapy oils in the house. It's a lovely wintery scent. You can use an electric diffuser, candle burner, make a room spray (diluted in vodka or another alcohol), or saturate something absorbent, then leave it near the radiator, etc. I think cinnamon is particularly good in this respect. Cinnamon is strong though, so I wouldn't use it on the skin, and take care not to spill it on varnished furniture undiluted. Same with orange - they get it out of the skins of citrus fruit so it's quite acidic.
One thing, though. Aromatherapy oils are quite powerful, so you should limit their use around babies and cinnamon is one of those which should not be used by pregnant women.
P.S. I second janet's suggestion of ginger tea. It's simple to make: take 15 slices of ginger root and boil them for at least 15 minutes in a pot of water. You can store it in the fridge for up to a week and reheat when required. Leave the ginger in it when you store it and the flavour will develop more. I chop and freeze the ginger afterwards for use in curries.
And talking of curries, I think a really spicy curry is another excellent remedy for a cold. Great for clearing the tubes and boosting the immune system.