Yesterday I start to read Test Driven Development in Microsoft.NET it's so great that I could not stop until the last page !!
It covers not only TDD but also it's the best implementation of Fowler's Patterns I've ever seen in the .NET platform.
Also I liked the way it uses TypedDatasets to represent the entities, the ADO.NET Hacks, and of course the design of the unit tests. The last thing I would like to mention is the introduction to the FIT framework to develop "Customer.Tests".
It's the best book I've read about .NET design. A MUST HAVE