Whenever Sheikh Abdul Aziz is asked to recommend books on Sufism or the Mevlevi tradition, his usual advice is that in his experience it may be better ‘to follow one's own nose’.  However, he also often recommends the following:

The Way of the Sufi by Idries Shah (Penguin Arkana 1968)

Beads of Dew – Histories of the Khwajagan, The Masters of Wisdom by Mawlana Ali ibn Husain Safi translated by Muhtar Holland (Al-Baz Publishing Inc 2001)

Love is the Wine by Sheikh Muzaffer Ozak edited by Robert Frager (The Philosophical Research Society 1999)

Living Presence by Sheikh Kabir Helminski (Penguin Putnam Inc 1992)

The Knowing Heart by Sheikh Kabir Helminski (Shambhala Publications Inc 2000)

And, of course, the many books by and on Rumi, including The Mathnawi of Jalaluddin Rumi translated by Reynold A Nicholson.