If you are interested in reading about Contemplative Prayer these are the books I have found helpful.
ST. JOHN OF THE CROSS
THOMAS MERTON
WILLIAM A. MENNINGER
CONTEMPLATIVE PRAYER and THE CLOUD OF UNKNOWING
WILLIAM A. MENNINGER
THE WAY OF CENTERING PRAYER
M. BASIL PENNINGTON O.C.S.O.
Author Unknown
Joseph Sitler not on Centering Prayer
Rediscovering Lectio Divina
THELMA HALL r.c.
Renewing An Ancient Prayer Form
M. BASIL PENNINGTON
HENRI J. M. NEUMAN not on Centering Prayer
THOMAS MERTON
A 30-Day Experiment in Listening to God
MAGGY ROBBINS & DUFFY ROBBINS
THOMAS KEATING
Secrets of Spiritual Maturity from the Desert Fathers and Mothers
Gregory Mayer
Fundamentals of Centering Prayer
CARL ARICO