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 Fall/Winter 2009 issue just arrived last week and is focused on online professional development and the use of Web 2.0 and social networking for professional development. Past issues have dealt with ways to do professional development with no budget, as well as making professional development more interesting and timely for educators.
Back issues are also available online.
It is from the publisher of Education Week, which also publishes Teacher Magazine and Digital Directions. All three are also great resources for educators.
I also wrote another article about Professional Development and resources.
UPDATE: The new issue (Spring/Summer 2010) just hit my mailbox today. It has some great new articles and ideas and of course the huge list of resources and providers.
This issue focuses on Response to Intervention topics, but also has much more in it.
It is not available online yet, but eventually will be on their site.
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.