The New Topping Book and The New Bottoming Book both were really great reads. I don't know that they necessarily taught me anything new, but I love the way the authors write together. Janet Hardy and Dossie Easton have several books on BDSM and Poly that are worth reading.

(Exciting sidenote, Janet Hardy is teaching for KinkEd Atlanta/Atlanta Dungeon in September!)

I personally found inspiration from a book called Wizard's First Rule by Terry Goodkind. A character called Mistress Denna... It's a fantasy novel, but if you've read it you'll get the parallel. (The tv show depiction was a horrible disappointment and all wrong so definitely read the book!)