I've noticed that most people I've spoken to about LINQ books have not been able to recommend one. The first batch that came out were usually just re-hashes of what you can find online and were based on the Beta bits of LINQ. This is usually a problem encountered whenever a new technology first comes out and is par for the course if you want the information at a bleeding edge pace.

I just wanted to recommend a book on LINQ that I have just recently been reading. It is "Pro LINQ - Language Integrated Query in C# 2008" by Joseph C. Ratz, Jr.

The book provides an introduction to LINQ as well as to the C# language enhancements that are used by LINQ such as Lambda Expression, Partial Methods and Anonymous Types. It then proceeds to cover specific LINQ implementations which includes LINQ to Objects, LINQ to XML, LINQ to DataSets and LINQ to SQL. The author took 17 months to write the book and it shows in the level of understanding that he seems to possess.

I find it to be written in a very clear manner with just enough repetition in each chapter to have things stick in your memory. A copy of the source code used in the book is provided online.

I have mainly been reading the LINQ to SQL section and that is what I'm basing my recommendation on.