Khan Academy provides free instructional videos (among many other things) for K-12 kids to learn about a variety of topics (the site currently boasts a library of over 2,600 videos!). You can read more about Khan or just dive into some awesome learning. Below, I've rounded up a few starter videos to give you a taste.
Khan Explains How it Works
A fun TED Talk. "First time I smiled doing a derivative!"
An "introduction to how banks make money and the value they (potentially) add to society."
Calculus: Introduction to Limits
Chemistry: Elements and Atoms
"How elements relate to atoms. The basics of how protons, electrons and neutrons make up an atom."
Computer Science: Introduction to Programs, Data Types, and Variables
Points to Khan for using Python, though we all know real men write in Assembler.
Astronomy: Scale of Earth and Sun
Just how big is the Earth? One nerd-jerk note from me: this video misuses the term "further." It should be "farther" when referring to distance.
Tell Your Khan Story
Do you use Khan Academy? Leave your thoughts and links to favorite videos and exercises in the comments.