eXtreme Programming (XP)
I think the XP philosophy is an extremely (no pun intended) valuable and worthwhile approach to programming. So much so that I decided to start my own list of resources on the subject.
eXtreme Programming Explained - Kent Beck
Just buy it.
This site is dedicated to software developers using JUnit or one of the other XUnit testing frameworks. We'll be adding more content and web-based services over time. Initially we'll be providing links to give you a one-stop destination to learn the latest information on unit testing.
Test-first coding - Kent Beck, IEEE, May 2000
Interesting challenege geared towards people with little experience in test-first coding. A complete set of tests is provided for un-written code. That's the challenge, you write the code. Gives an interesting introduction to what it means to write code to make tests pass.
Articles and resources on the concept, application and benefit of pair programming.
All I Really Need to Know about Pair Programming I Learned In Kindergarten - Laurie Williams and Robert R. Kessler. Communications of the ACM, May 2000.