Understand that I did not read too thoroughly this thread before I posted this, so if these books were already suggested then I do apologize. These are the books that are directly related to Paganism, Witchcraft, and Wiccan elements in general. I read a lot of supernatural romances that revolve around lycans, vampires, witches, all of which hold a Pagan undertone. If you ever want to discuss a good series NEVER feel shy to strike up a conversation with me because I absolutely LOVE to read.
Yasmine Galenorn writes excellent novels, and my favorites are her series "The Daughters of the Moon" which follows three half-breed Fae sisters through their trials and tribulations on both sides of the veil.
And then there is Anya Bast who also writes a fairly invigorating set of novels. My favorite is her Witch series which follows a Coven of elemental witches and their struggles against the Duskoff (another Coven with nothing but evil intentions for their magical abilities) and staving off an interdimensional war with the Daemon breed across the veil.
And then my favorite series, thus far, that directly relates to the demon element I am so drawn to is Jacquelyn Frank's "Nightwalkers" series. It is the most erotic series, but also the most romantic and I find myself lost in the novels. It is about the Demon race (which includes shapeshifters, shadowdwellers, and vampires alike) fighting to stave off a civil war amongst the Demon breeds, all the while keeping peace among all the supernatural races.
If you've read any of these novels be sure to let me know. There is also an excellent vampire series I've read, but chose not to waste your time with it here seeing as how this isn't really the forum for all of that. Of course they're all fiction, but if I could just find one person who's read them... I would be so excited. I always find myself forming a complicated bond with the characters and I want to know I'm not the only one.