Khan Academy

Free of charge, you can subscribe to Khan Academy on YouTube. From basic addition, to interpreting Shakespeare – Khan Academy provides thousands of lessons exploring a variety of concepts! New videos are added daily!

Crash Course

The Green Brothers (notably known as the VlogBrothers) developed Crash Course Education.  Crash Course and Crash Course Kids is comprised of hundreds of videos exploring sciences, history and math.  Using humor and genius analogies, the Green Brothers bring to life so many concepts that potentially could have been missed in the classroom.