Eight Essential Tools (link broken, so I removed the link) by Ron Snee, Quality Progress:
Ron is the co-author of 2 excellent books on Six Sigma:
- Six Sigma Beyond the Factory Floor: Deployment Strategies for Financial Services, Health Care, and the Rest of the Real Economy by Ron D. Snee and Roger W. Hoerl, 2004.
- Statistical Thinking : Improving Business Performance by Roger Hoerl and Ronald D. Snee, 2001. A great book on how to apply statistical thinking to improve business results. More details on Statistical Thinking.
and many articles: