Math from "1+1" through to advanced calculus. Physics, biology, chemistry, and finance are also covered with more being created all the time. All of them the work of one man - Salman Khan.
Khan Academy videos seem to break all the rules of educational videos. There is no on screen instructor - Salman Khan is just a voice over. Many of the videos have nothing but a black screen on which Salman draws and writes on using his offscreen graphics tablet. Some of the videos do have backgrounds that aren't just black. The chemistry videos may have an onscreen periodic table for instance. Even then the backdrops are for writing and drawing on.
He doesn't seem to work from a detailed script. He knows what he wants to cover and he gets to it. He makes mistakes and corrects himself. He uses phrases like "super duper strong" and other colloquialisms. He doesn't talk down to students or lecture endlessly. All the things that just "are not done" in most educational videos are the things that make these videos so accessible.
The collection is growing. The list of topics ever expanding. I don't know if Salman Khan will be able to continue doing this for as long as he wants. He started by using his own savings as he put together this free resource. Here's hoping he finds funding, donations, or grants and continues for a long time. Even if he doesn't continue much longer his obsession has already created an educational resource that is freely available and never going away.