How Stuff Works was started by a professor to provide people with clear and concise explanations of how the world works.  Combining videos, long form articles, slideshows, and quizzes, the How Stuff Works website is a great introduction to a variety of topics, especially topics that aren’t traditionally covered in a class curriculum (income tax, anyone?).  There is also an available network of shows and podcasts, such as the popular Stuff You Missed in History Class, that present this information in a lively and engaging manner.

Website: http://www.howstuffworks.com/
Subject: Science, Technology, Economics
Grade Level: 2-12
Price: Free