Great Links for Teachers
The Commons on Flickr
With thousands of images from over 50 museums and organizations that are free to use it is a great place to start when doing presentations for class.
TeachingBooks.net is a comprehensive database of popular titles for students k-12. In addition to providing basic information about the books, it also includes games, activities, and background information about the text.
Discovery Education provides images, videos and articles on a variety of topics to users.
Light bulb attribution Olivier Guin, from The Noun Project