These are books that I keep on my bookshelf and refer to quite frequently. They are listed in no particular order.
Permanent Magnet Design and Application Handbook - Lester Moskowitz Ferromagnetic Materials Structure and Properties - R.A. McCurrie Permanent Magnet Materials and their Application - Peter Campbell Introduction to Magnetism and Magnetic Materials - David Jiles Physics of Magnetism - Soshin Chikazumi Modern Magnetic Materials - Robert O'Handley Introduction to Magnetic Materials - B.D. Cullity Ferromagnetism - Richard Bozorth Permanent Magnets and their Application - Rollin Parker Magnetism Principles and Applications - Derek Craik
Corrections, additions, suggestions would be welcomed!