Focus on the Family asked its Facebook fan base what book after the Bible is the most influential in their life.  Given Focus’ audience, 85%+ plus of the responses were from women.  The informal survey isn’t representative of the full church, but the results are still informative.  My counting of the comments wasn’t scientific, so take it as an approximation of the responses:

• The Purpose Driven Life by Rick Warren: 5%
• The Battlefield of the Mind by Joyce Meyer: 5%
• The Shack by William Young: 4%
• My Utmost for His Highest by Oswald Chambers: 3%
• Mere Christianity by CS Lewis: 3%
• The Hiding Place by Corrie Ten Boom: 2%
• Crazy Love by Francis Chan: 2%
• The Left Behind Series by Tim LaHaye: 2%
• Hinds Feet in High Places by Hannah Hurnard: 2%
• Pilgrim’s Progress by John Buynan: 2%
• Jesus Calling by Sarah Young: 2%
• Experiencing God by Henry Blackaby: 2%
• The Five Love Languages by Gary Chapman: 1%
• Heaven is for Real by Todd Burpo: 1%
• The Case for Christ by Lee Strobel: 1%
• The Pursuit of God by AW Tozer: 1%
• Other titles: 64%

Observations
First of all, the top three books all have their own issues as described by the links above.  Secondly, if the list captures the most influential book in the lives of these Christians, the church is being held together by duct tape because many books on the list have little to no depth of content about God (e.g., the Five Love Languages).  Lastly, the Christian book industry marketing machine has taken over because only six books on the top list were written over 20 years ago.  For a list of better options, many that have stood the test of time, see books for new Christians, growing Christians and mature Christians or the recent recommended reading from the TGC Women’s Conference.  This informal survey ended up with a better result.