What's the differences between virtualization and cloud computing?

Many people will be confused by the relations and differences between virtualization and cloud computing. Following essays will clarify the nature of the two technologies.
1. Cloud is an operations model, not technology: http://news.cnet.com/8301-19413_3-10249486-240.html
2. Difference Between Virtualization and Cloud Computing: http://data-centers.in/virtualization-and-cloud-computing/
3. The Difference Between Virtualization and Cloud Computing: http://www.erpsoftwareblog.com/2010/08/the-difference-between-virtualization-and-cloud-computing/