A pretty well-written Salon article on eXtreme Programming. As an aside, I've been on a couple of projects that used (or tried to use) XP. When you can get the buy-in of customer and programmers, and you're not scared to fix the bits of it that don't work for you personally, XP works really well. Just, whatever you do, don't try to do XP without the full involvement of the customer. If you do that, you're doomed.

As another aside, Salon is the one website I've actually paid to subscribe to, purely because I believe it deserves to exist.