PHI DELTA KAPPA Publishers of Phi Delta Kappan, they are an international educational organization, provider of training, etc.
AOL on EDUCATION This searchable portal site covers the broad category of education, with reviews of some of the highlighted sites.
WEB66 Maintained by several divisions of the University of Minnesota School of Education, this site is highly rated by several publications and organizations. It is dedicated to introducing internet technology into schools. It provides background material, and suggestions for how to get started. The title is derived from the idea of exploring America by the old Route 66 (I still remember the TV program with Martin Milner and George Maharis -- I'm dating myself, but I did like red Corvettes). They try to maintain a list of usable sites, which you explore using their Web Mustang (the car, not the horse), but a caution: in my explorations, almost half of the sites on their list were not active. The others were useful, so it is still worth a shot.
Connections + Multi/Interdisciplinary a portal to a lot of very good and interesting sites, with lesson plans, activities, etc.
Teaching with Mysteries: I learned about this site from the Reach Every Child people. Mysterynet.com has a programs of using mysteries to teach critical thinking, reading, writing and higher-order thinking skills. Might be usable in a variety of curricula. Has lesson plans.
Educational Web Resources page maintained by the Department of Education at the Catholic University of America: I have found this useful both as an introduction to using the web, and as an link to a number of good resources (many of which are referenced directly and indirectly within this web site).
LEARNER ON-LINE A site maintained by the Annenberg/CPB (Corporation for Public Broadcasting) coalition to provide on-line educational resources (New 990913)
For a more complete list of professional organizations in the field of education, try the Educational Association subsite of the U.S. Department of Education
(990913))