I take echinacea and goldenseal. Straight echinacea doesn't stop the bug once it's established, but EG will shorten the duration of your colds.
Do you take golden seal regularly?
I have heard it has adverse effects on the liver. Especially when coupled with certain hobbies such as bottom of the beer/liquor bottle inspection.
I have no citation or anything but as with many of these herbs, anecdotal seems to be the norm.
It also doesn't hurt to take zinc on a regular basis along with the echinacea and goldenseal. They are a powerful preventive measure.