I don't take any specific "hair" vitamins, mainly the ones I always took before learning about haircare. I tried biotin earlier in the year and MSM and stopped shortly afterward because of side effects (even though I drink a lot of water).
I stick to what works for the health of my body like vitamins b, c, iron, calcium and the food such as flaxseed oil, spirulina, sea vegetables, lots of water and a healthy diet. One exception might be the grapeseed extract I take which keeps the immune system very strong and assists in the beauty of hair.