Mythic Island, though I think she still works with other publishers too. You can find her Wikipedia entry here and her books on Amazon here.
I first learned of Rust Nestvold through the Online Writing Workshop for Fantasy, Science Fiction, and Horror (OWW). I can't remember if we ever critted each other's work or not there. She's had short fiction published in venues such as Strange Horizons, Asimov's Science Fiction, and Realms of Fantasy. Her work has been nominated for the Tiptree and the Nebula. Learn more about Nestvold and her work on her website, Wikipedia, and Amazon.
Andre Norton is one of the giants of the genre, with over 300 books to her credit and an award named after her. Some of her work was published under a male pseudonym, and she legally changed her name from Alice Mary Norton to Andre Alice Norton to be more marketable to boy readers. My first encounter with her work was Moon of Three Rings, which I read in middle school. (Years later, I bought a copy, which you can see in the picture below.) I've also read part of the Elvenbane series, Tiger Burning Bright, some of the books in the Magic Sequence, and part of the Trillium series. I read one of the books (The Crystal Gryphon) in the Witch World series, but it wasn't the first one in the series as I thought. You can learn more about Norton on her website, Wikipedia, and Amazon.
Do you have any other authors for the N part of this series? Please feel free to add them to the list.