E. M. Bounds
http://www.ccel.org/ccel/bounds?show=worksBy
R. A. Torrey
How to Pray
http://www.ccel.org/ccel/torrey/pray
Andrew Murray
With Christ in the School of Prayer
http://www.prayertoday.org/classics/murray-prayer/index.htm
The Prayer Life
http://www.worldprayerfoundation.com/The%20Prayer%20Life.pdf
J. C. Ryle
A Call to Prayer
http://www.fivesolas.com/callpray.htm