The Gateway to 21st Century Skills
A huge, searchable collection of educational resources.

EDSITEment
Many interesting lesson plans in a variety of areas from the National Endowment for the Humanities.

Education World
Another large, searchable site with  a great deal of original content including many lesson plans, ideas for integrating technology, informative articles, and a search engine for education Web sites only.

The Educator's Reference Desk
Formerly Ask ERIC, this is one of the most comprehensive sources for lesson plans. It contains over 2000 unique, teacher-submitted lessons.

NEA Lesson Ideas
A searchable collection of lesson plans for all subjects and grade levels.

ThinkFinity
A partnership providing high quality, standards-based Internet content for K-12 teachers including lesson plans, interactive learning tools, engaging content, panel-reviewed links, and professional development resources.

Discovery Education
Many high-quality lesson plans.

Read/Write/Think
Many high-quality, language arts-related lesson plans for all grade levels.

ArtsEdge
A program of the Kennedy Center for the Performing Arts, ArtsEdge offers high-quality, standards-based, interdisciplinary lesson plans.

Education at the Getty
A list of units and lesson plans lesson plans available from the J. Paul Getty Museum.

National Archives and Records: Teaching with Documents Lesson Plans
Teaching activities and lesson plans based on primary documents in the Archives. Lessons are correlated to national standards for history, civics, and government. 

Teaching with Historic Places
From the National Registry of Historic Places. Click here for a chronological index of available lesson plans.

Illuminations
Created by the National Council of Teachers of Mathematics, this site offers multi-media mathematics investigations, reflections on teaching, links to the best panel-reviewed mathematics web resources and Internet-based lesson plans all linked to the updated NCTM Principles and Standards for School Mathematics .

SMILE Program Lesson Plans
Nearly 200 lesson plans from IIT organized by the following categories: Geometry and Measurement, Patterns and logic, Probability and Statistics, Recreational and Creative Math, Practical and Applied Math, Arithmetic, Graphs and Visuals, Algebra and Trigonometry, and Miscellaneous.

Franklin Institute Science Lesson Plans
Elementary science lesson ideas; most are constructivist.

Smithsonian Education Web
Great lesson plans for art, language arts, science, and social studies.

Social Science Education Consortium
Lesson plans for both the elementary and secondary levels from the NCSS.

Xpeditions
From National Geographic. See also National Geographic Geography Lessons and Ideas.

Yale-New Haven Teacher's Institute
This site contains units developed by Fellows participating in the Institute's seminars. These units are intended primarily for use by Fellows and their colleagues who teach in the New Haven Public Schools, but they also provide concrete examples of ways in which teachers have drawn material from Institute seminars for use in their own school courses. The units are indexed both alphabetically and by year of development.

United Nations Cyber School Bus: Curriculum
Lessons and units on the UN, peace education, poverty, world health, cities, human rights, etc. New topics and units are periodically added.

Teachers-First Classroom Resources and Lesson Plans
Lesson plans and links organized by grade level and subject (from A and E Network).

MrDonn.org
Perhaps the best privately-maintained education site on the Net with lesson plans in most subject areas.

Internet Activities for Foreign Language Classrooms
Lesson plans for a variety of languages, but mainly for Spanish and French. See also Foreign Language Lesson Plans and Resources.

Lesson Plans from the National Core Knowledge Conferences
A good collection of lesson plans organized by grade level. Many appear to be cross-disciplinary and constructivist in nature.

TeacherLINK
An excellent site from Utah State University with lesson plans and units on Africa, celebrations (including holiday lesson plans), famous persons, NASA instructional units, and many social studies units and lessons.

Lesson Plan Central
Links to many lesson plans organized by subject.

Lesson Plans Page
Another large collection of lesson plans categorized by subject.

Utah Education Network
Hundreds of units organized by subject area and grade level.

Teacher Spot
Lesson plans, help for beginning teachers, and many education resources.

TeachNet: Lesson Ideas
Still another great source for lesson plans.

CEC Lesson Plans
More than 600 teacher-created lesson plans as well as web guides and web-based teaching resources. Lessons are organized by subject and grade level. Check out the "miscellaneous" lesson plans for ideas on on self-concept, conflict resolution, and other affective topics.

Academy Curriculum Exchange
Nothing fancy, but a user-friendly site organized by grade level and subject area.

Lesson Plans from the Rock and Roll Hall of Fame and Museum
Many high-interest lesson plans for a variety of subjects and grade levels. 

Curriculum Archive
Lesson plans organized by grade level or search by topic.

A to Z Lesson Plans
Lesson plans for all grades. See also Teacher Stuff A to Z: Theme Pages.

Education Place Lesson Plans.
An excellent source for locating lesson plans by topic (e.g. pets, weather , etc.).

Adprima Lesson Plan Page
An excellent site with instructions for lesson plan writing and links to lesson plan sites.

Kodak Lesson Plans
Lesson plans for a variety of subjects and levels which use photography.

Awesome Library
Annotated lesson plan links by subject.

KET Teachers' Resources
Links to lesson plans and resources by subject.