xUnit Test Patterns: Refactoring Test Code, by Gerard Meszaros (Addison-Wesley Signature Series, May 2007) is nothing short of FANTASTIC!
As I'm reading through the book, I keep saying to myself "Yes!" and "Aha!" over and over again. This book is very appropros for me right now because I'm dealing with a team that has a legacy codebase and is just trying to develop automated tests and they don't yet have a lot of training or experience refactoring or in automating their own tests, or the xUnit-style tools, much less using all of them together.
This book is EXACTLY what the doctor ordered for my current situation. It covers the basics of test automation styles and frameworks using harnesses and drivers, data-driven as well as other styles and the challenges to be addressed, especially with test setup. It has comprehensive coverage of 68 patterns and an awesome website at http://xunitpatterns.com/ which does a far better job of depicting them than I could on this blog.
If you're trying to get a small group of folks to learn how to do agile-style test-automation and refactoring, this is the book with all the patterns and insight you will want to convey to your team.