This book has to be the first on anyones list who wants to clicker train their horse.
It starts off, talking about the basics of clicker training, how to get your horse to touch a target and then progress to leaving their head on it longer and then - C/T-ing a horse to do pretty much anything!
The book takes you through a few examples of what has been done in the past but encourages you to think about what you would like to teach, break it down into small peices and then work your way through it. C/T can be used for almost anything, a horse standing still whilst you are mucking out around him, getting a horse to load itself, a horse holding its leg up for you to bandage it.... the possibilities are endless, you can even use it to improve your ridden work.
If you're interested in C/T then buy this book!