Ecstasy in Darkness by Gena Showalter
Ava Sans, working for Alien Investigation and Removal along with her best friend, Noelle, is bloodthirsty, smart, and insecure about her own worth. Victor McKell is an arrogant vampire who can stop time, and he's currently on AIR's most wanted list.
Throw in an alien queen with some sort of virus-spreading ability that can destroy everyone on the planet and McKell's desire to learn how to walk in daylight, as some other vampires are doing, and you have a thing or two besides romance and bonding to keep Ava and McKell busy.
This is easily one of my favorite Showalter books, partly because of the friendship between Ava and Noelle and the snappy dialogue from most of the characters. How many books have two best friends betting on whether the hero will remove the penis or the heart of the other guy who is lusting after his woman? Snappy and fun with an edge.
My overall personal rating of Ecstasy in Darkness is a B+.