Black Magic By Moonlight (Harry Potter/Anita...
AU after Order of the Phoenix (no Horcruxes, but Voldie has already been defeated at the beginning of the story) and book 12 of Anita Blake.
Harry is exhausted after finally defeating Voldemort and finishing school, so Draco sends him to his family's house in St Louis to get away from it all before the Ministry can co-opt him into a publicity tour. Of course Harry manages to walk straight into trouble and when it's trouble that attracts the attention of Anita Blake, Federal Marshal and former vampire hunter, it has to be bad.
Vampires, wereleopards, werewolves, demons and more await Harry as he struggles to stay alive in a world that is very different than at home, and figure out exactly what his relationship is with Draco at the same time.