I'm becoming a fan of David Pogue's Missing Manual series. This book, and his iPhone: The Missing Manual are very detailed, clearly written, and full of non-obvious helpful advice.

This volume is hefty, weighing in at some 800+ pages, and it explores nearly every corner of the Leopard operating system. I bought a Macbook two weeks ago, coming back to Macintosh after about 10 years away, and this book has helped me come up to speed very quickly. Man has Apple leapfrogged Microsoft with OS X. Nearly every aspect of the operating system is extremely well thought out, and though you'd never discover a tenth of it's power by exploring on your own, it turns out that David Pogue is an excellent guide. He points out all the features you'd ever use, most of the time with explanations that help make good sense of everything.

Recommended.