The Professional Barista's Handbook is a very efficient training manual for espresso, and features some great information on brewing too (plus a couple pages on tea ... why?) I was impressed with how concise it is, and how useful it will be for the home enthusiast.
Best of all, it cuts to the chase and shows the core methods for achieving great extraction without making you read too much theory. It also avoids being too specific in showing just one technique. In other words, read this book and over time you surely will develop your own variations. That's the way it should be.
Scott Rao has 14 years practical experience so the Handbook combines essential theory with a lot of behind-the-bar insight. And it's not full of a bunch of froo-froo beverage recipies. It's from a small press, essentially self-published, 100 pages on nice thick stock with some excellent illustrative photos and graphs, and a bit spendy at $45. But you could buy a 250 page book with half of the essential information that you would have to trudge through. If you want a great book that is more expansive in focus and technical, get the Illy Espresso Coffee book above. But here is all the essential information in a book you will truly use!