Taurine is another vitamin that improves concentration. It's actually not a vitamin, it's an amino acid.
I would like to warn people about taking mega doses of vitamins though. I once took large doses of magnesium for my anxiety and concentration problems. A few hours later, I was dizzy, nauseated and spent half of the night vomiting. I found out later that these are symptoms of magnesium toxicity.
Vitamins and minerals can be toxic in large doses. It's not a good idea to take a bunch of vitamins without even knowing if we are deficient in them or not. Most of us do get enough vitamins from our diet.