Kiss of a Demon King by Kresley Cole
Book number 6 in the Immortals After Dark series, Kiss of a Demon King by Kresley Cole is my favorite in the series so far.
This is the story of Rydstrom Woede, fallen Demon king who has been seeking the return to his throne for 500 years, and Sabine, Queen of Illusions and the half-sister of the usurper of Rydstrom's throne. The only search Rydstrom has been on longer than the one to recapture his throne is the 1500-year search for his destined mate, who, of course, is Sabine.
I hate giving away stories, so I'll just say that the instant sexual compatibility doesn't translate into a smooth ride to trusting each other. When the time comes, though, Rydstrom and Sabine are both willing to make the ultimate sacrifice for each other. Yes, the women in Cole's books are at least as strong and interesting as the men. No damsels waiting around to be saved when there are other options in these books! And they're also just as apt to save their men as to be saved.
I have to admit that I fully expect the story of Nix, which seems to be coming as a book written with Gena Showalter since Nix's current plan is to visit Showalter's Lords of the Underworld in Budapest, to be even better than this installment! I also have high hopes for Sabine's half-sister, Lanthe, being featured in a future book.
I should note that the sex scenes are pretty hot and heavy--and well-written-- in all Immortals After Dark books.
Also, you don't have to read all of the books in the series, or even the books in order, if you decide to start reading. Characters do reappear from book to book, but you won't feel "lost" if you lack their background information. You receive at least a little intro, enough to fit with the story in progress, on who the character is at his/her appearance.
My overall personal rating of Kiss of a Demon King is an A-. I have this book on my personal list of all-time favorite romance novels.