For openings, my favorite manuals are chess openings for white / black, explained by Alburt et al. 

Some middlegame possibilities at various levels:

50 Essential Chess Lessons by Steve Giddins

https://web.archive.org/web/20140708100833/http://www.chesscafe.com/text/review534.pdf

Chess Strategy for Kids by Thomas Engqvist

http://www.gambitbooks.com/pdfs/Chess_Strategy_for_Kids.pdf

Starting Out: Attacking Play by James Plaskett

https://web.archive.org/web/20140708101549/http://www.chesscafe.com/text/review467.pdf

Simple Chess by Michael Stean

https://web.archive.org/web/20140708104258/http://www.chesscafe.com/text/review400.pdf

Amateur's Mind by Jeremy Silman

https://web.archive.org/web/20140708094419/http://www.chesscafe.com/text/ammind.pdf

Chess Secrets: The Giants of Chess Strategy by Neil McDonald

https://web.archive.org/web/20140708092313/http://www.chesscafe.com/text/review620.pdf

Chess Strategy for Club Players by Herman Grooten

https://web.archive.org/web/20140708101926/http://www.chesscafe.com/text/review696.pdf

Chess Training for Post-beginners by Yaroslav Srokovski

https://web.archive.org/web/20140712013538/http://www.chesscafe.com/text/review945.pdf

Chess Strategy: Move by Move by Adam Hunt

https://web.archive.org/web/20140708093249/http://www.chesscafe.com/text/review890.pdf

How to Reassess Your Chess (4th ed.) by Jeremy Silman

https://web.archive.org/web/20140708095832/http://www.chesscafe.com/text/review769.pdf

Understanding Chess Middlegames by GM John Nunn

https://web.archive.org/web/20140627012322/http://www.chesscafe.com/text/hansen154.pdf

Winning Pawn Structures by GM Alexander Baburin (1998)

https://web.archive.org/web/20140718055446/http://chesscafe.com/text/wps.txt

Understanding Pawn Play in Chess by GM Drazen Marovic (2000)

https://web.archive.org/web/20140708110136/http://www.chesscafe.com/text/review249.pdf

Dynamic Pawn Play in Chess by GM Drazen Marovic (2001)

http://theweekinchess.com/john-watson-reviews/books-of-many-flavours

Winning Chess Middlegames, An Essential Guide to Pawn Structures by GM Ivan Sokolov (2009) https://web.archive.org/web/20140708091955/http://www.chesscafe.com/text/review676.pdf

Pawn Structure Chess by GM Andrew Soltis (2013)

https://web.archive.org/web/20140708101523/http://www.chesscafe.com/text/review908.pdf

Chess Structures - A Grandmaster Guide by GM Mauricio Flores Rios (2015)

"There is also masses of stuff in the book that made me go 'Oooh!' and 'Aaah!' so I think it will have the same effect on you! In particular, I loved Rios' exposition of White's plan of exerting queenside pressure against Hedgehog systems. I'd seen one of the games he quotes in his chapter but I'd never remotely made any link to a structured way of fighting the Hedgehog structure, so this chapter was a real eye-opener for me ... In conclusion, warmly recommended. Lots to learn!" - GM Matthew Sadler

The Power of Pawns by GM Jörg Hickl (2016)

"The didactic concept of the book is admirable. Each chapter defines the structures, explains the typical characteristics and shows the plans for both White and Black. The reader participates by assessing positions and invariably receives useful tips for practical play." - FM Harry Schaack

Python Strategy by Tigran Petrosian

http://sagarteacheschess.blogspot.com/2015/09/python-strategy-book-review.html

Petrosian’s Legacy by Tigran Petrosian (1990)

https://web.archive.org/web/20140708103409/http://www.chesscafe.com/text/review309.pdf

Petrosian: Move by Move by Thomas Engqvist

"Engqvist gives us a rare treat and a genuine, sympathetic understanding of one of chess' greats who nowadays tends to gets lost in the shuffle!" - Michael Ciamarra (2014)

Grandmaster Chess Strategy by Jürgen Kaufeld & Guido Kern

https://web.archive.org/web/20140708093410/http://www.chesscafe.com/text/review812.pdf

Various endgame study possibilities discussed at:

http://theweekinchess.com/john-watson-reviews/endings-endings-endings

http://theweekinchess.com/john-watson-reviews/the-end-game-comes-before-we-know-it

http://theweekinchess.com/john-watson-reviews/theres-an-end-to-it-all

https://web.archive.org/web/20140708103149/http://www.chesscafe.com/text/review594.pdf

https://web.archive.org/web/20140708105702/http://www.chesscafe.com/text/review645.pdf

https://web.archive.org/web/20140708234309/http://www.chesscafe.com/text/review704.pdf

https://chessbookreviews.wordpress.com/tag/chess-endgames-for-kids/

Before buying any particular book, I suggest going to the publisher site to see if it is possible to view a sample.

http://www.thechessmind.net/blog/2010/1/30/a-brief-review-of-carsten-hansens-back-to-basics-openings.html

https://web.archive.org/web/20140627031504/http://www.chesscafe.com/text/hansen76.pdf

http://www.gambitbooks.com/pdfs/Understanding_the_Chess_Openings.pdf

https://web.archive.org/web/20140626173432/http://www.chesscafe.com/text/hansen128.pdf

http://www.gambitbooks.com/pdfs/FCO_Fundamental_Chess_Openings.pdf

https://web.archive.org/web/20140708093123/http://www.chesscafe.com/text/review756.pdf

https://web.archive.org/web/20140627132508/http://www.chesscafe.com/text/hansen173.pdf

It was part of a seven part series of chess books. Here is a review of three other books in the series:
http://seagaard.dk/review/eng/bo_beginner/ev_winning_chess.asp?KATID=BO&ID=BO-Beginner

Good Chess Books for Beginners and Beyond...

https://www.chess.com/forum/view/chess-equipment/good-chess-books-for-beginners-and-beyond

Understanding Chess Middle Games by GM Nunn

Fundamental Chess Ending by Muller

Fundamental Chess Opening

This is the best book in the market!!

Elementary Geometry for College Students 6th Edition

 Thanks all for the book recommendations. 

Possibly of interest:
https://www.chess.com/article/view/the-best-chess-books-ever
https://www.chess.com/article/view/chess-books-and-youth-vs-old-age
https://www.chess.com/article/view/chess-cyborg-chess-teachers-and-chess-books

Good Chess Opening Books for Beginners and Beyond...

https://www.chess.com/forum/view/chess-equipment/good-chess-opening-books-for-beginners-and-beyond

You say intermediate.  If your over the board rating is anywhere from 1400 to 2000, I recommend the Yusupov series.  Orange books first, then blue, then Green.  Each book is 24 lessons, 216 lessons all told.  I have heard from a friend of mine who is 1800 that 1 lesson takes 60 to 90 minutes at the orange level.  Blue and Green will take longer, so expect to spend some serious time.

Forcing Chess Moves (Hertan) is an extremely good book for improving your calculation skills. 

What a great list!  Thanks, folks!

LOL I'm not sure the OP will be helped by any of these books... "Back to Basics - Tactics" would be the best suit for him right now, judging by his rating. 

I have no idea why I recommended "Forcing Chess Moves" w/o looking at his rating first. 

http://www.qualitychess.co.uk/ebooks/Build-up-Your-Chess-1-exceprt.pdf

https://web.archive.org/web/20140708103321/http://www.chesscafe.com/text/review699.pdf

http://www.qualitychess.co.uk/ebooks/Build-up-your-chess-2-excerpt.pdf

http://www.qualitychess.co.uk/ebooks/Build-up-Your-Chess-3-exceprt.pdf

https://web.archive.org/web/20140708103659/http://www.chesscafe.com/text/review778.pdf

http://www.qualitychess.co.uk/ebooks/Boost-Your-Chess-1-excerpt.pdf

http://www.qualitychess.co.uk/ebooks/BoostYourChess2-excerpt.pdf

http://www.qualitychess.co.uk/ebooks/BoostYourChess3.pdf

https://web.archive.org/web/20140708103149/http://www.chesscafe.com/text/review834.pdf

http://www.qualitychess.co.uk/ebooks/Chess-Evolution-1-excerpt.pdf

https://web.archive.org/web/20140708085817/http://www.chesscafe.com/text/review843.pdf

http://www.qualitychess.co.uk/ebooks/Chess_Evolution_2-excerpt.pdf

http://www.qualitychess.co.uk/ebooks/Chess_Evolution_3-excerpt.pdf

http://www.qualitychess.co.uk/ebooks/Revision&Exam1-excerpt.pdf

https://web.archive.org/web/20140708233537/http://www.chesscafe.com/text/review585.pdf

https://www.newinchess.com/Shop/Images/Pdfs/2722.pdf

https://web.archive.org/web/20140708111520/http://www.chesscafe.com/text/review637.pdf