Here are some well-known Christian books that can be found for free online and can aid in Bible study:
"The Bible" - The Bible is the foundational text of Christianity and can be found in many different translations online for free.
"The MacArthur Study Bible" by John MacArthur - This study Bible includes notes and commentary from John MacArthur, a well-known Bible teacher and pastor.
"The Bible Study Guide" by J. Vernon McGee - This guide includes outlines, summaries, and discussion questions for each book of the Bible.
"The Bible Study Handbook" by Lindsay Olesberg - This handbook is a guide to studying the Bible, including tips and methods for personal study.
"The Bible Study Companion" by Dr. Warren Wiersbe - This companion includes study notes, insights, and background information for each book of the Bible.
"The Bible Study Guide for All Ages" by Kay Arthur - This guide is designed for all ages and includes study questions, activities, and teaching plans for each book of the Bible.
"The Bible Study Guide for Beginners" by Dr. James A. Cox - This guide is designed for those new to Bible study, and includes tips and methods for personal study.
"The Bible Study Guide for Teens" by Dr. Joe White - This guide is designed for teenagers and includes tips and methods for personal study.
"The Bible Study Guide for Women" by Elizabeth George - This guide is designed for women and includes tips and methods for personal study.
Please keep in mind that these are just a few examples and there are many other Christian books available online for free that can aid in Bible study. It's always a good idea to consult with a spiritual leader for recommendations.