A few months ago I wanted to look into LINQ to SQL and grabbed a copy of Essential LINQ
The new language features of .NET 3.0 are covered which enable LINQ in the first place so if that’s new for you no need to buy another book. All LINQ operators are explained using LINQ to Objects followed by a very thorough discussion of LINQ to SQL. Mapping, stored procedures, modifying objects and how you can plug into the system with extension methods. After diving deep into LINQ to SQL there’s only a very small description of the Entity Framework or LINQ to Entities. Which is probably, in hindsight, the biggest issue you can have with this book since it’s now the de facto standard of data access promoted by Microsoft. The book finishes with another in depth discussion of LINQ to XML which was new to me and just like LINQ to SQL you’ll be an expert by the end of the chapters.
So to wrap it up, the book reads like you’re being thaught by a very good teacher. If you want to make sure you know your basic LINQ this is the one you need.