Khan Academy is a self-paced, free, source of online lessons that provides an easy path for students to jump in and begin learning about any subject that they choose.
Ted-Ed is full of educational videos on a variety of general education topics that can be accessed for free. Not only are there motivational speakers on Ted, there are also topical videos, often less than ten minutes each that are full of important information.
Wyzant- Helps students sharpen skills and offers study materials for English, Math, Science, History, and Spanish
Smithsonian Education Students provides educational resources and information, lesson plans, field trips, and interactive activities based on Smithsonian museum collections and research.
DocsTeach -Access thousands of primary sources — letters, photographs, speeches, posters, maps, videos, and other document types — spanning the course of American history
Illuminations has online math activities, lessons, and skill practice for Grades Pre-K-12
Wolfram Alpha- Computational Knowledge Engine
Desmos- Free online graphing calculator with example and tutorials.