On the left hand side there are a number of internet links and catalogues. There are also links to some fun and interesting weblogs that I follow.
In addition to these I would like to add the following sites:
The Accredited Leaders wiki and the Diploma in Educational Leadership wiki are found at http://sites.google.com/site/accreditedleaders/ and
I have looked at the open course content at Yale University for a few years now. They continue to upgrade and expand their services and are well worth a look http://oyc.yale.edu/
The best evidence synthesis material from the New Zealand Ministry of Education (MoE) at http://www.educationcounts.govt.nz/publications/series/2515 has a number of reports, including The University of Auckland findings on School leadership and student outcomes - Identifying What Works and Why: Best evidence synthesis iteration (BES).
Also from the New Zealand MoE comes a site dedicated to professionally developing educational leaders - http://www.educationalleaders.govt.nz/
The Australians have an interesting site about Principals leading and learning at http://www.principalsaustralia.edu.au/servlet/Web?s=157573&p=LL_LEADERSHIP_STANDARDS