I recently started seeing a holistic MD, and asked her to prescribe some vitamins for me. I had been on about 3 years worth of Rx prenatals, and figured I'd just keep going with something high quality. She told me that she really didn't want me to take vitamins--I needed to get my RDA from healthy foods, so that my body would correctly assimilate the nutrients to match my body's needs. So many vitamins out there are showing signs that taking them outside of food sources can actually do a lot more harm than good for your body.
I went with her advice, I don't see any negative effects to my health, and it forces me to concentrate on getting the right nutrients in my diet. (Before, I'd just say, "Enh, I take a multi-vitamin...that ought to be enough," and I was wrong.) The only thing I am taking right now is a flax seed oil supplement, and I understand even that isn't as good as it could be. Fish oil would be a better way to get my Omega nutrients.
You might also check out the Health boards for more information. Good luck!