I have not read these books all the way through, but glanced over so my descriptions might be a little off.
Expert F# 2.0 by Don Syme
Programming F#: A comprehensive guide for writing simple code to solve complex problems by Chris Smith
Real World Functional Programming: With Examples in F# and C# by Tomas Petricek & Jon Skeet
Expert F# 2.0 &
Programming F# are good overview's of the language and could be used as a reference.
So if you are smart like Thorsten(kaefer) & gile and can pick up the language and run with it. These two would be a good book.
I am going to read
Real World Functional Programming This book really would not be good as a reference, but looks like a good tutorial.
This book spends alot of time on teaching functional programming aside from the language.
There is more code in the first 2 chapters of
Expert F# 2.0 &
Programming F# than the first half of
Real World Functional Programming.
It also shows the functional style in a C# to show the benefits of accomplishing the same tasks with a functional vs. Object Oriented language
So this one looks better for people who have never programed in a functional style and look at problems in a object oriented manor.