I just finished reading
The Quantum Universe: Everything That Can Happen Happens by Brian Cox and Jeff Forshaw.
I greatly enjoyed reading this work, and it definitely expanded my knowledge about quantum mechanics and the principles behind it. But, this book is definitely not for the faint of heart, it hovers on the far edge of popular science, with the already not so light subject of quantum mechanics described and discussed thoroughly, with more than a flavor of mathematics. Many of the theories behind quantum mechanics are described in depth and when possible experiments confirming the theories are discussed.
I originally bought this book to understand the Higgs boson a bit better. And indeed, the last chapter of the book deals with the Higgs boson and explains how it gives mass to all the other particles. I did not get the feeling, however, that the theory behind the Higgs boson was as well and in depth explained as some of the concepts toughed upon earlier in the book.
Overall, I would recommend the book for those interested in quantum mechanics in general, but probably not as a first book to be read on the subject.
I have some hopes for better understanding the Higgs boson by reading
The Particle at the End of the Universe: How the Hunt for the Higgs Boson Leads Us to the Edge of a New World by Sean Carroll, but consider the current price still a bit steep (and have plenty more on my TBR list).