Echinacea is one of my favorite preventatives. It aids the immune system in fighting infections like the common cold. Its validity has not been proven, but I take it when there's 'something going around', and it works for me. I highly recommend taking it regularly when you are vulnerable to exposure.
Echinacea should not be taken indiscriminately, however: your system will become immune to its effects, and there is possibility of liver damage from overuse.
