Boundaries: When to Say Yes, How to Say No to Take Control of Your Life: Henry Cloud, John Townsend
This book was highly recommended to me and I'm finding it very enlightening. It's not specifically about procrastination, but it addresses a lot of resistance issues that many of us struggle with. It is written from a Christian standpoint with lots of Bible quotes and whatnot, so if you're not into that, this book might not be for you. But if you're ok with the religion part, it's an excellent book.