Coursera - an education platform that partners with top universities and organizations worldwide, to offer courses online for anyone to take, for free.
Educational Testing Service - Comprehensive focus on testing and test preparation, financial aid, etc.
ERIC - Educational Resource Informational Clearinghouse Statistics and data on everything related to education.
Learning A-Z - A variety of free resources.
NAESP - National Association of Elementary School Principals
NASA -related K-12 learning projects
Smithsonian Institution - This site offers activities, resources, perspectives and an electronic tour of its museums.
T.H.E. Journal's Road Map to the World Wide Web for Educators - This is an excellent directory listing sites of both specific and general nature which are of interest to educators.