Dr. Haykin serves as co-editor, along with Joel Beeke, of the Reformation Heritage Book series 
"Profiles in Reformed Spirituality". The newest volume in the series is by Thabiti Anyabwile and focuses on the piety of Lemuel Haynes. To promote this volume and the series of which it is a part, Reformation Heritage Books is randomly giving away five free sets today to those who sign up at Challies.com.
This is a great set. The volumes are multifunctional. That is, they are the perfect, non-intimidating introductions to people, doctrine, and practice of the reformed tradition. They make excellent short readings for stimulating thought and devotion. They are also good for class texts for giving students an affordable entry point into a given person and time period both primary and secondary treatments in one small book.
If you don't win the set, You can order the complete set or individual volumes at Reformation Heritage Books.