Raw eggs are good too, I do that as well, but only a few times a week. I don't like to over-do it on the eggs.
And I'd seriously consider switching to a better food than IAMS. That's likely one of the major reasons you have a dog with a lot of dandruff.

My old Rottie was on IAMS (years ago) because my vet said it was an "awesome" food. Yeah right! LOL Glad I know better now, but my dog too had a lot of dandruff, scratched like mad and goobery eyes and such.
If you have feed stores close (most big chain pet stores dont carry these) look into Canidae, Innova, California Natural, Eagle Pack, DVP.......much better foods. Or if you buy at Petsmart, their brand Authority Harvest Baked (not regular, make sure it's the harvest baked) that is ranked right up there with Canidae, but quite a fair bit cheaper. Ingredients list is good. In Windsor I think it is about $35 for a 40lb bag, and actually cheaper I believe than IAMS.