Summerfield's "Programming in Go" is several years old but still the best I've come across. Below is a review regurgitated from Barnes and Noble if you're interested:
...The author spends his time away from the libraries, covering the core of the language. By the nature of this approach the matter is dense, but it also gives the author ample time to discuss best practices, for instance:
"...[i]ncidentally it is a Go convention that functions that have channel parameters have the destination channels first, followed by the source channels [in the function definition]..."
Many of these best practices stem from conventions found in Go's own source code, which happily, the author is well acquainted with. Learning a language by isolating its syntax and analysing idioms and conventions is effective for those willing to persevere, and "Programming in Go" abounds in such detail.
Ideally, "Programming in Go" should be paired with a textbook which focuses on use-cases. Balbaert's "The Way to Go" is such a book, but sadly, is not nearly so well written as Summerfield's. In any case, "Programming in Go" is the book for those searching for a solid understanding of Go's fundamentals.
