Amended the original post, and also a bump.
Bloodsucking Underworld - Vampires exist, though no one would have you believe that. They don't sparkle, they are fierce, sexy predators of the night. Their most influential run humanity. The human in this pairing finds this out after they fall for a vampire, they are inadvertently dragged into a world they never knew of before.
A Fanged Marriage - Similar in concept to the first listed idea, difference is this one is set back hundreds of years. A young human is married to another she had never met, this person is wealthy and mysterious. After arriving at the secluded home the human discovers that their spouse are in fact a vampire. The human is dragged into the vampire underworld, a very dangerous place.