Edited by 1love4ever - 3/29/14 at 1:20am
There are supplements for lactating women that you can find in upscale natural foods grocery stores like Whole Foods or Sunflower Market (if you live in the SW). You can take just a multivitamin with or without iron and a calcium supplement with vitamin D. You can get into taking all kinds of specific vitamins. You don't have to take any vitamins at all.
I took a multivitamin without iron and a calcium supplement with vitamin D.
That said, I've read on kellymom that you don't have to take any supplements. I eat fairly healthy, but I know my diet isn't perfect and I certainly don't eat enough oily fist so for me I think that the DHA is especially important. So what you take may also depend on your personal need for "extra" nutrients.
Here is some info on DHA. Dr. Hale recommends that women not take DHA supplements. Dr. Hale wrote the book on drugs in pregnancy and breastfeeding.