Via .NetSmoothie, LINQ to DataSets - the Missing Manual:

"This morning I discovered that Fabrice Marguerie and his co-authors have published a bonus 47-page chapter of their book “LINQ in Action”, all about this very subject. The chapter is called “Working with LINQ and DataSets”, and they have made a PDF version available online for FREE download from the Manning Press website." -- Richard Bushnell

Andy Warren links to the Free LINQ book from MS Press:  Introducing LINQ.

On thesame page are also books about ASP.NET AJAX and Silverlight v1.0

Help.Net has a review of the new book, Pro LINQ: Language Integrated Query in C# 2008. The money quote: "I do hope that my review will encourage you to buy this book because not only is it the first one on the subject, but because it covers almost everything you need to know on the subject."