C# 5.0 in a Nutshell: The Definitive Reference – by Joseph Albahari and Ben Albahari – cover most of the language specifics of C# 5.0, with plenty of chapters covering the new async, threading, etc.
A lot of people seem to see this as more of a reference than a tutorial, but I didn't know almost anything about C# and still found it competent as such (I do have plenty of experience in other languages, though). The use of LINQPad for quickly being able to quickly try out samples (and change them as you want) is pretty great.
It is also quite impressive how many of the newest C# features were available in Chrome back in 2005 (a pascal for .net by Remobjects, now called Oxygene).
I highly recommend the book, but keep in mind that it only covers the language, not the other framework you will probably need (such as Winforms, WPF or ASP.NET).
