How to create and show a ranking based on Alexa of a wordpress network?

Hello folks,

somebody knows how could we create and show a ranking based on Alexa, which include blogs of a wordpress network and anothers blogs from others domains?

The idea will be to make automatically a ranking in a page similar to http://www.technorati.com/blogs/top100/
but for the blogs of a network and include other external blogs.

Thank you in advance.

Jorge