Halfway to the Grave by Jeaniene Frost

Book One in the Night Huntress series. Half-vampire Cat spends her nights flirting with the undead - and killing them when they make a move. She's pretty good at it, too, until she meets Bones, a vampire bounty hunter who gets the drop on her one night and captures her. Rather than kill her though, Bones tricks her into an unlikely partnership where he's the muscle and she's the bait.