I just completed "Effective C#, 50 Specific Ways to Improve your C#" by Bill Wagner and I must say I really liked it. This 300 page book shows how to write better code by applying 50 different "commandments". Even if you have been doing C# development since the first beta, like me, you probably will still learn from this book.
So for anyone interested in improving their C# (and VB.NET too B.T.W.) and write code that is correct and executes faster, I can recommend this book!