Vinegar - Mix 250ml grape vinegar with 2-3 liters of warm water. Set aside.
Shampoo and condition hair as usual with fresh warm water and rinse with normal warm tap water. After you have finished, immerse your clean rinsed hair in half the solution for a few minutes, allowing the solution to completely cover all of your hair and scalp. Comb through and then pour remainder over your hair. You can rinse again with fresh water if you like for the smell but it really won't remain after hair is dried.
Repeat two or three times a week and dandruff should be gone in a week or so.