The Artima book by Odersky is the bible, and so you need that one.

For reference, I like http://naildrivin5.com/scalatour although it's 2.8 rather than the current 2.12.

For style guide, I'd go with Li Hiayo's blog, notably the Strategic Style series: http://www.lihaoyi.com/post/StrategicScalaStylePracticalType...