An article on the subject from one of my favorite blogs:
Science-Based Medicine Another Negative Study of Vitamins
And I agree with what Snowy and others have said - best to get your vitamins from your diet. Supplements can help in certain circumstances, if you have a lack of a certain vitamin in your diet, or some medical condition.
Herbal supplements are 90% crap, and there isn't enough research for most of them to determine which is the crap and which isn't, though that's getting better. If an Herbal supplement *does* work, then they'll isolate the chemicals involved, put it out in purified form, and call it 'medicine'.