Do not take any myself. About the only vitamin supplement I might seriously consider taking might be Vitamin D during autumn/winter if I lived up North, but provided you have a diet that is only on nodding acquintance with a recommended diet, you are probably getting enough vitamins.
For those who have an underlying medical condition. or a poor nutrition it might be worth taking it.
You may feel more energised taking multivitamins because of a placebo effect, poppie - If you genuinely are getting a clinical benefit from the iron, that might indicate an underlying anaemia, which might be worth checking out...