Not a definitive list by any means! Please add your favourites;
"Counselling for Toads - A Psychological Adventure" by Robert de Board, great for teens and adults
"Clean Your Head" by Tim Box
"Before You Know It" by John Bargh
"The Expectation Effect" by David Robson
Healing Beyond Pills and Potions" by Steve Bierman
"Lost Connections" and "Stolen Focus", both by Johann Hari
"Responsibility Rebellion" by Kain Ramsay