My primary goal is to learn Scala. The primary reference (Programming in Scala) assumes the reader already understands functional programming and its associated terminology (such as point free code). Real world Haskell has good explanations of functional programming concepts but the language is too unusual to allow easy mapping to Scala.

This book has good explanations of key FP concepts. It avoids the common pitfall of FP books that are essentially self referential and do not provide a starting point familiar to an OO developer.

The C# and F# examples are easily understood from a Java and Scala point of view, respectively.

I would really like to see a book that follows the same approach and material but using Scala.