Succubus on Top (Georgina Kincaid, Book 2) by Richelle Mead
I had forgotten how much I enjoyed the first book until I picked up this second one!
Georgina is a succubus - she drains life energy from her sexual partners/victims. And she's in love with a human - which means she can't have sex with him without draining away some of his life. And if that's not enough, now she's dealing with someone dealing "otherworldly" drugs, problems at the bookstore, and on top of that, her friend Bastion (an incubus) comes to town and needs her help.
This book has lots of steaminess, action, and humor - more than enough to keep you reading late into the night!