Which vitamin supplements should I be taking?

If your diet is irregular and not as "healthy" as it should be, you MIGHT - or might NOT - benefit from a good multivitamin. You don't need to buy anything expensive. Just go to Walmart or Costco and buy a good general purpose multi-vitamin, a generic version of Centrum Silver works well, and take one per day. If you have a vitamin deficiency, that'll take care of it. You don't need to do more than that.