Books for Intermediate Players
https://web.archive.org/web/20140708112708/http://www.chesscafe.com/text/review943.pdf
http://www.gambitbooks.com/pdfs/John_Nunn's_Chess_Course.pdf
https://web.archive.org/web/20140627012322/http://www.chesscafe.com/text/hansen154.pdf
http://www.gambitbooks.com/pdfs/Understanding_Chess_Middlegames.pdf
https://web.archive.org/web/20140708234309/http://www.chesscafe.com/text/review704.pdf
http://www.gambitbooks.com/pdfs/Understanding_Chess_Endgames.pdf
While GM John Nunn is a highly regarded chess author, his books are targeted to an "advanced" audience, i.e., advanced intermediate and above, as ELO 1600 and above. Players below that level would be advised to read books appropriate to their current skill level.