Here are some free online teaching services:

Khan Academy: Khan Academy offers a useable, well organized interface. Also managing many courses from around the web, Khan Academy covers all the topics required at high school level( and above.)

PBS: At PBS, you’ll find videos on arts and entertainment, culture and society, health, history, home and how-to, news, science, nature, and technology.

YouTube: The videos you’ll find here range from academic lectures to professional development classes and speeches from teachers around the world, and let’s you create your own educational videos.

Howcast: This site offers short videos on just about anything you want to know about, including style, food, technology, recreation, fitness, health, finance, and education.

Teaching Channel: You have to register to use, but registration is free. Click on the Video tab and you’ll have access to more than 400 videos on topics in English language arts, math, science, history/social sciences, and the arts.