Khan Academy : Consider using these tutorials for flipped classroom.
Library of Congress: Find lesson plans and more that meet Common Core standards, state content standards, and the standards of national organizations.
Lesson Plans : Tons of lesson plans for middle schools. Search by grade level or subject area.
Middle School lesson plans: Almost 60K resources, including activities, worksheets, games, lesson plans, flashcards, puzzles, posters, assessments and other ideas for you to use with your 6-8 grade students.
Smart Exchange : Search for ready to use lessons that work with your smart board.
Fact checker for the internet: This link has several interesting sections that provide a wealth of research and discussion opportunities. An archive is also available. If a student or teacher needs a starting page to find resources, I definitely recommend this site.
Extend students geography awareness by challenging them to answer the five daily questions posed at GeoBee Challenge. The questions are taken from the National Geographic Geography Bee.
Map Machine is an interactive tool to explore your world with map themes, data, and tools for customizing your map.
Explore Daily Grammar's Lesson Archive to find a new grammar lesson every day. The site features nearly 450 lessons on topics ranging from adjectives and apostrophes to prepositional phrases and verbs.
Online textbooks : Free and copyright friendly textbooks for k-12 educators. Can be downloaded as pdf or e-pub format.
Big history project: Ask the big questions about our Universe, our planet, life and humanity. Explore where we are going in the future and challenge your students to develop the skills and knowledge they need to get there. Provides and excellent glimpse of 13.7 billion years on Earth.