Related papers to my own work which I highly recommend:

2007:

• Venkatesh Upadrista. Experiences on Agile Implementations. March, 2007.

2002:

• Steffen Schäfer and Peter Kutschera. Applying Agile Methods in Rapidly Changing Environments. July, 2002.

2000:

• Kent Beck and Dave Cleal. Optional Scope Contracts: How to use XP for fixed price contracts. May, 2000.
• The file has been downloaded from the extremeprogramming yahoo group. If you're a member of the group you can access the file there directly.