Education Week Teacher is a great, free, resource for teachers. The website has articles, teacher blogs, news, forums, professional development resources, and much more.
Topics cover all aspects of education, from lessons to curriculum to classroom management to assessment and more.
The articles are well written and very informative. Some are even written by some of the teachers in my PLN (like Larry Ferlazzo).
Education Week also produces the PD Sourcebook (free resource for professional development)