Because of an early health problem (a hemangionoma) I started feeding my girl a mixture of herbs (nettle, chlorella, parsley, burdock, turmeric, dandelion, bilberry extract) and oils (olive oil or coconut oil), topped with yogurt. this is her breakfast several days a week. She really likes it.
As an unintended consequence her coat is quite wonderful, I got rid of any vestiges of dandruff/flaking, and she sheds a little less than she did (which is like saying the shedding went from a blizzard to a snowstorm, but every bit helps).
I buy the herbs in bulk and grind/mix them myself, and it's pretty cheap -- hugely cheaper than the ready-made mixes that the holistic vets sell.
As part of all this I had her allergy tested and found that she was allergic to a lot of things in the better brand dog foods that should help with the coat -- flaxseed, fish protein, barley grass. Just an FYI in case you're doing all the right feeding things and still having coat problems.