Reddit reviews Programming in Scala: A Comprehensive Step-by-step Guide

Well, Python is by no means a functional language. But, if you know Java and want to learn functional programming, I would recommend that you learn Scala.

Scala runs on the JVM, you can use all the same Java libraries that you use today, and it lets you slowly transition into a functional style. A good way to do this is to get the staircase book and go through it somewhat in order. It's ever-so-slightly out of date with respect to the new Scala release, but the differences are small enough that it shouldn't get in the way of learning.

After you do that, if you want to have a lot of the same brain-bends that Haskell gives you, then you can learn how to use the scalaz library, though this is really something that you want to know the language itself quite well for, and it's by no means required to be highly productive in Scala.

Programming in Scala, co-written by Scala's creator, is the most detailed and authoritative book on the language. Highly recommended.

I also bought Pollak's Beginning Scala. It's a much slimmer book that tries - and, in my opinion, succeeds - to be a crash course in Scala's best features.

It's important to note that Scala 2.8 final is expected soon (2.8 beta pre-release is already available), so you might wish to wait for updated editions of Scala books. Scala 2.8 brings some important improvements and breaks the backward compatibility in some minor ways.

I read the one from Martin Odersky: http://www.amazon.co.uk/Programming-Scala-Comprehensive-Step-Step/dp/0981531601/ref=sr_1_1?ie=UTF8&s=books&qid=1269246979&sr=8-1
and the one from Dean Wampler.

The Wampler one is shorter and a bit more critical of Scala, but in my opinion the Odersky one is better for starters.

It's surprising that the unpublished book came up before the published one, but here ya go http://www.amazon.com/Programming-Scala-Comprehensive-Step-step/dp/0981531601