Kathy Schrock's Guide for Educators - Probably the best of the indices for educators. A working school librarian collects this ever growing list of internet resources. Cyberbee - is an excellent commercial site with lesson plans and other resources. Classroom Connect - certainly one of the best resources I've found for general knowledge. A great place to start.
Information is well catagorized and qualified.
The Apple Learning Interchange maintains a learning library for lessons and resources. This is NOT an Apple only resource. An index of lesson plans and ideas for teachers. The Educational Technology Journal Educom - Educause is a nonprofit consortium of higher education institutions that facilitates the introduction, use, and access to and management of information resources in teaching, learning, scholarship, and research. International WWW School Registry - Most complete of the current lists I've found.