The Teacher Professional Development Sourcebook is a great resource for teachers and administrators. It is published twice annually, for free, and contains a huge amount of resources.
Each issue includes articles, news, tips, ideas, research, resources, a calendar of professional development activities and more, all about professional development and continuing education. The back of the sourcebook is a type of yellow pages (even though they are white) with a directory of products, services, resources, and more related to professional development and continuing education. The directory is organized by type, topic, and subject area.
The Spring 2001 just arrived yesterday and is focused on real-world learning, authenticity in education, ELL issues, reading and writing, learning walks, and much more.
Past issues have dealt with ways to do professional development with no budget, social networking and social media in education, Web 2.0 resources for PD, as well as making professional development more interesting and timely for educators.
Back issues are also available online.
You can apply for a free subscription to the Teacher Professional Development Sourcebook.
I also wrote another article about Professional Development and resources.
The site has back issues online, as well as a ton of articles and resources, ranging from assessment and discipline, to PBL and PLN's, to administration and ELL/EFL. This is definitely a site to add to your favorites.