I have heard apple cider vinegar on scalp does wonders? Never tried it though.
Most persistent dandruff is actually seborrhea. Seborrhea is caused by a fungal infection; that's why Nizoral works so well.
However, Selsun Blue also seems to kill the fungus pretty well (or any shampoo whose active ingredient is selenium sulfide).
My advice? Pick up a bottle of a selenium sulfide shampoo or Nizoral (whichever is cheaper); use it 3 times/week for two weeks, then twice a week. Use a mild shampoo the other times you wash your hair. When using selenium sulfide or Nizoral, massage the shampoo into your scalp at the beginning of your shower, leave it on the scalp the entire time, then rinse it off at the end. At first it will seem to make the problem slightly worse, then it will get better.
If that doesn't work, try mixing a salicylic acid containing shampoo one-to-one with a selenium sulfide containing shampoo (you can get travel bottles to use for this). Use it twice a week, as above.
If that doesn't work, see a dermatologist.
Ugh I had dandruff From about 12 yrs old until high school...I've also been battling seborrhia for the past five years or so...its an ongoing battle...
Recently I've had it occur behind my ear and on my eyebrow as well...the doctor has had me on tricinoclone creme (spelling?) since it started...
I can never get my scalp to clear up 100% and it Always comes back.