Steve Freeman and Nat Pryce (creators of the JMock mock object testing tool, consultants, TDD teachers, and all around smart folks) are writing a book! It's entitled Growing Object-Oriented Software, Guided by Tests, and they're putting up draft versions of chapters on their blog. I'm looking forward to reading it, in particular to learn more about how they use mock objects to evaluate their tests and create better object-oriented designs.
I had good fortune to pair with Steve for a morning and I learned a lot and got some great objective (no pun intended, or is it?) feedback. Thank you, Steve!
I've also used and passed around Nat's blog entry on Test Data Builders at a few coaching engagements; it's a great way to start thinking about setting up your test data in a clean fashion.