I Hate You, Don't Leave Me is a good resource I think
Borderline Personality Disorder: A Clinical Guide by Gunderson
Understanding and Treating Borderline Personality Disorder: A Guide for Professionals and Families by Gunderson and Hoffman
Mentalization-based Treatment for Borderline Personality Disorder: A Practical Guide by Bateman and Fonagy (good info though you may not agree with this treatment approach, I'm not sure how I feel about it)
Also, I LOVE Millon's personality theory, so I recommend checking out his books on personality pathology in general. I don't think you can find a book just about his theory of BPD, sadly.
Really I think research articles are better than books for BPD. There is a wealth of studies out there.