Team Code Review & Design Sessions
XP is about getting the right values and practices and maximize it to the extreme. CODE it's essential and practices like pair programming and unit testing / test driven are a must have. I don't think they are enough, so i like to work a lot with team code reviews and design sessions. As a Software Architect I found such techniques very effective specially in scenarios that the team is beginning with XP and don't do pair programming effective or the team technical skills have a huge contrast. I'm not against pair programming of testing BUT this old fashion techniques work as well.