Karen Marie Moning's Fever series. I am actually not all that into the Fae part of fantasy/paranormal fiction, but this was truly an excellent series. Try not to fall in book-love with Jericho Barrons.
Karen Marie Moning's Fever series takes you through the adventures of MacKayla lane. Her sister was murdered in Ireland and she travels there to find information about her mysterious death. This is technically classified under romance but it's really more of a fantasy.