books for the average player

Any good chess books for a player considered average strength ?

Without having a clue as to what YOUR definition of "average strength" is here goes:

Logical Chess Move by Move and The Most Instructive Games of Chess Ever Played by Irving Chernev

500 Master Games of Chess by Dr Tartakower & J DuMont

My System by Nimzovitch if you only get one book on this list this is the one!

Practical Chess Endings by Chernev and/or another book by Keres, same title

Catastrophe in the Openings by Yakov Neishtadt

1001 Checkmates by Fred Reinfeld

One or more middlegame books by Fine, Euwe or especially Romanowsky

Many players also like instructional books by Jeremy Silman, but I haven't read any of his works so all I can say is see what other respondents have to say about him and many other authors I haven't read.

I would have to say if you only get 1 book get How to Reassess Your Chess by Jeremy Silman. I have both that and Nimzo's My System and I must say, Silman's book is infinitely more easy to read. It is a great book that taught me a lot, and it was very instructive, and at times entertaining. 

I would also recommend Bobby Fischer's My 60 Memorable Games and Mikhail Tal's game collection book.

I would actually say that the algebraic version of Chernov's Logical Chess Move by Move is more valuable to a beginner than My System or Reassess your Chess.

Silmans endgame book should be your second book.

Catastrophe in the Opening is this book free in pdf or djvu format somewhere.

The Art of the Middlegame (Review: http://blog.chess.com/SimonSeirup/the-art-of-the-middlegame-by-keres-amp-kotov)

The Middlegame (Review: http://blog.chess.com/view/review-the-middlegame-book-one---static-features-by-m-euwe-and-h-kramar)

How to Reassess your chess (Review: http://blog.chess.com/SimonSeirup/book-reivew-how-to-reassess-your-chess-4th-edition)

Fundamental Chess Endings

If you see it for 'free' in pdf or djvu, it has been acquired illegally and the author was not compensated for it.