Honestly, for a preacher this book is a goldmine. Not only for teaching you to be better at your craft, but because it's also chock full of great stories and illustrations.
Made to Stick
Finished Made to Stick by Chip & Dan Heath the other day. This is definitely a book worth checking out. Not a Christian book per se, but every preacher/teacher should read it. It's a book about what it takes to get ideas to stick with people and becoming a better communicator. In short, their premise is that in order for an idea to stick it needs to be simple, unexpected, concrete, credible, emotional, and incorporate stories.