A must-read for everyone is Logical Chess Move by Move, by Irving Chernev. If you haven't read it, do so!
The "Winning Chess" series by Yasser Seirawan is also very good. The first three in the series are Play Winning Chess, Winning Chess Tactics, and Winning Chess Strategies. Look into those.
If you want a book that covers several different aspects of chess theory, look into The Complete Chessplayer, by Fred Reinfeld.
Hope that helps.
I want to buy a chess book that will help me with the theory of chess and useful tactics or openings. I would be delighted if any of you could recommend a good book that includes these things.