Chess Openings Book

I would like your recomandations on the best books one can find on openings, opening theory, different variations of openings, etc.

I'm looking for something of good quality, preferably written by a GM, with as much details as possible. I'm not just looking for an opening database, I want a book which explains the moves, and the logic behind them. The "why's ?" "why not's ?" and "what if's".

I realize there is a lot of material on the internet, but I can't be sure of the quality of those books. I've seen books being praised by some reviewers and trashed by others, so I'm a little bit confused.

FCO: Fundamental Chess Openings by Paul Van Der Sterren.

http://www.amazon.com/FCO-Fundamental-Paul-Van-Sterren/dp/1906454132

Lots of good reviews on Amazon. I like it because it's so readable.