Ok, so I agree with everyone else on the fact that you should be getting the majority of your nutrients from food (and along that vein that what you eat is the basis of health). But I do supplement with a few things because even though I tend to buy organic produce and naturally raised (meaning pastured, not feed-lot or confinement) meats, the mineral and vitamin profiles of food have changed over the last 100 years due to modern agriculture and foods aren't as "rich" as they used to be.

I take a daily multivitamin. I take omega 3s (I don't eat much seafood). I take Choline (a B vitamin that helps you process high-fat diets like mine). And I take vitamin D (since I work inside all day). The vitamin D I have actually seen a big difference with in my ability to not get sick as often and my mood is generally better. I will probably also be adding a magnesium supplement in the near future to help with leg cramping at night (I don't eat as many leafy greens as I should either).

Maybe I'm peeing it all out, maybe not. But I personally have noticed a difference in my health (placebo is possible) so I will continue to take vitamins. And eat well.