Free Technology for Teachers (blog):  http://www.freetech4teachers.com/

Reports each week describing several free tools and suggestions for their uses in the K-12 classroom.

Classroom 2.0 (community):  http://www.classroom20.com/

Large and growing community of teachers interested in using social media in education.  Forums, links, webcasts, good sources of information.

Internet 4 Classrooms (portal):  http://internet4classrooms.com/introducing_i4c.htm

This site is a portal to many resources for and about using the internet in the classroom.  This page describes it; click on "Home" to go to the main page.

ISTE - International Society for Technology in Education:  http://www.iste.org/

Organization for educators engaged in improving learning and teaching by using technology in education (all levels).  Lots of information, links, books, on the site.

eSchool News: http://www.eschoolnews.com/

Technology news for K-12 educators

Carol's Diigo list of 21st Century Classroom Links

http://www.diigo.com/list/furchner/21st-century-classroom

(Use this as a basis for exploring Diigo, too!)