There are some really exceptional chess books out there. "The Amateur's Mind" by Jeremy Silman and "Reassess Your Chess, volume 4" by the same author is another outstanding book.
If you like the French Defense, "The Modern French" is excellent.
Former world champion Max Euwe also has some outstanding books out there.
That being said, there is a lot of excellent material on Chess.com
Just thinking.....
If you want the maximum benefit out of studying. Use a real board and pieces, as opposed to an online board and pieces.
I would like to quote Mark Dvoretsky, from his interview with Peter Doggers on Chessvibes:
"Sometimes people ask questions like: what should I do, this or that? Should I play the main lines or some side lines, should I concentrate on tactics or on positional play, should I play more or study more, and so on. There is no answer to such a question. The right answer is: you should do both in some proportion. But the main problem is proportion – this proportion depends on the personality of each person, so again there's no clear answer. It's a matter of the player himself, or his trainer to decide what is correct in this concrete case. To ask such a general question 'what is better, this or that' is just the wrong approach."
"It is essential for any chess player to read good authors."
"There are many really good books, and I recommend people to distinguish them from bad books and to read just good books, no other books."
"Chess can be seen as a practical skill, an occupation like riding a bicycle, or playing the piano, or something like this. How to improve? Like in any other area. You should follow good patterns, so study good examples, good patterns, and train yourself. Very simple. Studying good patterns means studying good books, good articles, try to get the best out of it, this will help you to do best yourself. Train yourself, in any practical area. I do it in all my lessons, with all my students. It's a natural part of normal chess work: train yourself. Because chess is not just knowledge, it's also skills."
http://www.chessvibes.com/?q=reports/the-dvoretsky-interview-part-1/
http://www.chessvibes.com/?q=reports/the-big-dvoretsky-interview-part-2
http://www.chessvibes.com/?q=reports/the-big-dvoretsky-interview-part-3
Another quote: "... A remark like 'games are rarely decided in the opening' does not really do justice to the issue. ... even if an initial opening advantage gets spoiled by subsequent mistakes, this doesn't render it meaningless. In the long run, having the advantage out of the opening will bring you better results. Maybe this warning against the study of openings especially focuses on 'merely learning moves'. But almost all opening books and DVD's give ample attention to general plans and developing schemes, typical tactics, whole games, and so on. ... For almost every player, the best advice is to simply study what you like most. ... I do think that some trainers overrate the benefits of studying endgames and act in a somewhat patronising way by advising us to study the endgames we might never get on the board, instead of the openings we are sure to have on the board all the time. So if you do not enjoy studying endgames, there is no reason to worry too much about it. This, after all, is what 'no-opening-theory' trainers advise us, albeit with the subjects changed: they want to let us play the opening on insight alone, but the endgame with exact knowledge. So you might try it the other way around. ..." - IM Willy Hendriks (2012)
[COMMENT DELETED]