In response to a request, here's my list of my top 5 favorite books. Feel free to toss some in the comments section if you feel I missed out.
1. Silman's Complete Endgame Course - Jeremy Silman
Some say you should start by learning the endgame first. If you did then there is no better book I've seen to get you there. The book is broken into chapters for class E, D, C, B, and A players, then Experts, Masters and beyond. No matter what your level of expertise it's always good to brush up on material that's meant for people below you, and likewise a class C player with a class A player's endgame knowledge won't be class C for too long. At the very least you will know how to draw or win simple rook and pawn endings, a talent that is surprisingly uncommon. Silman's writing is fantastic, there are lots of pictures, and for 99% of us it's the only endgame book you need.
2. 1001 Winning Chess Sacrifices and Combinations - Fred Reinfeld
A fantastic puzzle book divided into different themes of combinations by chapter - forks, discovered check, double attack, etc. Read it, solve the puzzles that you can, then read it again. Then again. A long time ago the Massachusetts Chess Federation (or whatever it was called) was hawking this book along with its companion 1001 Brilliant Ways to Checkmate with the guarantee that if you read each book a few times and your rating didn't go up 200 points then they would refund your money. Needless to say they are still on my shelf.
3. My System - Aron Nimzowitsch
One of the most accessible and memorable books in chess, My System is a master course in the fundamentals of positional thinking. In this it is superior to any number of other such books in the wry sense of humor of the author along with the compelling imagery he uses to describe his ideas. One I'm remembering offhand is a quote about favorable exchanges 'falling like ripe fruit into your lap' if you maximize your position rather than seeking exchanges specifically. That thought alone has brought me some victories.
4. Zurich International Chess Tournament, 1953 - David Bronstein
Another timeless classic, this book details the 300 (!) games played at the candidates tournament in 1953 to determine who would face Botvinnik for the World Championship. The games are of outstanding quality, the tournament itself was very tense with Reshevsky getting as close as anyone until Fischer would ever get to toppling the Soviet machine. Bronstein annotates all games, and does so in a way that sadly does not get repeated much - with minimal mind-numbing variations, and commentary that is light but brings incredible insight to the positions with minimal effort. Indeed, the game seem very easy, would that it were true.
5. The Nominees:
I really could not think of a fifth book that matches the first four in the impact they've had for me, but here's a few that are worthy of consideration:
Understanding Chess Move by Move - John Nunn
Tal-Botvinnik 1960 - Mikhail Tal
Art of Attack - Vladimir Vukovic
Revolution in the 1970s - Garry Kasparov