It is available my latest book about LINQ in .NET 4.0. You can find it here. It is a complete reviewed edition starting from the previous one. We (I and Marco Russo) wrote 6 new chapters and updated 5 already existing chapter.
The result is a book that I really like. Hope you will like it, too. Now I’m working on the SharePoint 2010 Developer Reference, which will be released in early 2011.
Enjoy your reading!