Every once in a while you run into a reference that should be on every C# developers desk. The C# 3.0 Cookbook is just such a reference. It covers a ton of everyday how do I's for every thing from Exception handling to LINQ queries. Each chapter is broken down into a series of Problem, solution, discussion so you get a clear understanding of not only what problem is solved and how, but more importantly, why it was solved the way it was.
Some of the solutions have been around since .Net 1.0 and others are new to 3.0. If you are looking for a great reference, this is the one.