I've also read about "Harmonic Experience". The reviews left a good impression about the book. But one particular review said the book was good for someone already experienced in harmony, or for those who want to learn why music sounds good. He said that the book is more "spiritual" than scientifical (which should be the strongest/weakest point of this book).If you assure me that this book covers the same ground has a traditional harmony book/course should cover I will favour it. However, if this is an only an enlightement for someone who have already learned harmony, it's not what I'm looking for.Thanks for the comments so far!
I like the approach and I tend to think similarly to how they present the material, so that is helpful. It's laid out nicely and the organization makes sense, making the concepts easy to focus on and grasp.
I would recommend the Piston book as well as the Schoenberg one. There is a book on Harmony by Diether de la Motte which I recommend as well.