You know - I take a multivitamin every day, 1000mg of Vitamin C, and a mineral supplement (as I started to have hair and nail issues around about the 80lbs lost mark!)... I also take Echinaechea when I feel a cold coming on.
The best thing I did for myself recently was switch from hard tablet vitamins to capsules - the body absorbs more of the goodness that way!
I am also a fan of Cold FX, even though it is very expensive - I only use that when I am doing a show.
Hope that is of some help!