This is a short list of resources (websites and books mostly) that I have read/do read/participate in on the topic of Extreme Programming.  My list is VERY long and I didn't want to put it all up, so I listed the most relavent items.  You might not see some other popular sites/books, but most of them can be found from any of the websites listed below.  This is just part of the list I maintain for myself, and its plenty to have to keep up with.  Instead of listing all the TDD resources I maintain, I linked over to Darrell Norton who already has a great list of resources on TDD put together.

Extreme Websites

• Extreme Programming Yahoo Group
• Ron Jeffries’ XProgramming
• Don Wells’ Extreme Programming
• Pair Programming
• Exploring Extreme Programming

Agile Websites

• The Agile Alliance and Agile Manifesto
• Agile.Com

Refactoring Websites

• Martin Fowler’s Refactoring
• Refactoring Yahoo Group

Test Driven Development Websites

• TestDriven.Com
• Test Driven Development Yahoo Group
• A ton of links from Darrell Norton

Extreme Books

• Extreme Programming Explained 1st Edition
• Extreme Programming Explained 2nd Edition
• Planning Extreme Programming
• Extreme Programming Installed
• Extreme Programming Pocket Guide
• eXtreme .Net
• Other Extreme Programming Books on Amazon

Refactoring Books

• Refactoring: Improving the Design of Existing Code
• Refactoring To Patterns
• Other Refactoring Books on Amazon

Test Driven Development Books

• Test Driven Development
• Other Test Driven Development Books on Amazon