The answer to this question probably depends on where you are in your chess journey and what you really want to achieve.
The books that helped me the most were ones that fueled my interest in chess. Some of these like "Endgame: Bobby Fischer's Remarkable Rise and Fall" by Frank Brady were not even instruction books. But they piqued my interested, provided great entertainment or spurred me on.
Early on I really enjoyed Yassir Seirawan's books. These books were entertaining and gave me a pretty good foundation to build on. Three of his books took me about a year to get through. I saw improvement in my playing. Start with "Play Winning Chess" then try others by this author.
After that I would recommend tactics books or software. Lots available. I liked "Tactics Time" and "Back to Basics: Tactics". Doing puzzles can get dry, so I just do a few (maybe up to 10) then read something else. Ten minutes each day can make a big difference, or so I found.
Strategy books were not much help for me. I could have a terrific strategy and still lose spectacularly due to a missed tactic or bungled opening. I read several strategy books that were way beyond me. I would have been better off reviewing the beginner books, practicing tactics or just playing live games. Plus, they were work to me and not as enjoyable as other materials.
I read a few annoated game books and I like these, but I find them to be only marginally instructive. For me, this is entertainment. I try not to think too hard about it, but rather enjoy the artistic combinations and witty commentary. I think about the people playing the game, the history, world events at that time, etc. "Logical Chess" by Chernev is a good example of this sort of book.
Chess is a hobby for practically all of us, so try not to take it too seriously. If you go on the hunt for THE book that will give you a radical ratings boost, you're going to be searching for a long time. You already have lots of books, just try a few and see what interests you. If it turns into work, but it down and move on. Hobbies should be fun you know.
Which chess books have you studied and how did they have an affect on your overall development? And which ones would you recommend? Right now I'm in possession of Capablanca Move by Move by Cyrus Lakdawala, Pawn Structure by Andrew Soltis, Three Matches of Anatoly Karpov by Mikhail Botvinnik (Written in Russian), Bobby Fischer Teaches Chess, and a slew of the Tournament Player's Handbooks by Batsford, a first edition print of Morphy's Games of Chess by Lowenthal, as well as the encyclopedia of openings by Batsford titled Batsford Chess Openings explained by Kasparov and Keene. So far Pawn Structure, Capablanca Move by Move and Bobby Fischer Teaches Chess have had the biggest affect on my game and I believe it is due to their interactive structure and explanations rather than dry chess notation. One book that I am not fond of is Morphy's Games, mainly because the chess notation is written in an older format and difficult to grasp at first, but all in all it is a quality book and that would be my only criticism of it. So, what books have helped you and which ones would you recommend?