Harrington on Hold 'em, Volume 1, is the definitive book for anyone interested in learning No Limit Hold 'em tournaments. The book is filled with strategy, theory, odds, and tons of sample hands to help advance a poker player's No Limit tournament performance. Everything is written in a clear manner and all of the advice is excellent.
I've read this book twice now and it has definitely improved my tournament play; I'm sure I would still be busting out early in tournaments if I had never picked this one up. Volume 1 only focuses on the early and middle stages of tournament play, so players that are interested in further understanding of the strategy should also pick up Volume 2.
The best thing about the book is the in-depth analysis that goes into every sample hand; the reader can easily see how advanced the thinking of these poker pros is.