I picked up "Concurrency in Go" (http://amzn.to/2xiGSmi) a few weeks ago. Total game changer on the concurrency part. It totally explains the whole model with a ton of examples and concurrency patterns. I'm still wrapping my head around a lot of it, but my day job code has improved significantly since even my first pass through the book. Highly recommend.

I'm still trying to wrap my head around garbage collection and other optimizations that we can make at a lower level. Go is so fun, though.