NavPress (the Navigators) has made available "Speak Up with Confidence: A Step-by-Step Guide for Speakers and Leaders". Carol Kent has been around for a number of years and is well known as a capable writer. This book is available for your Kindle, Nook, or via CBD's proprietary reader apps.
Abingdon Press has made "Shrouded in Silence" by Robert Wise available for the Nook and for CBD's proprietary reader apps. Robert Wise also has been around for awhile and is known for his thrillers and mysteries - this book falls into this genre.
David C. Cook has another book available, "Dreaming of More for the Next Generation: Lifetime Faith Ignited by Family Ministry" by Michelle Anthony. I know nothing of this author, but Sandra worked for a day care center operated by the the publisher during our first three or four years of marriage. They do know their stuff and I would trust their editors to choose good material.