I'm always looking for resources that can help principals. One of my favorite websites is The Principals' Partnership (www.principalspartnership.com), sponsored by the Union Pacific Foundation. The site includes lots of useful articles including a set of over 200 Research Briefs (http://www.principalspartnership.com/library.html) that provide information about all of the important topics faced by principals. The briefs can be easily downloaded for your use.
There are also a couple of articles at the site that share tools for improving instruction. They include First Things First (www.principalspartnership.com/feature908.html) and Improving Instructional Quality (www.principalspartnership.com/feature308.html).
I hope you find these resources helpful. Let me know of any great resources you find for helping principals.