iTunes U

iTunes U is a great source for free content for your classroom:
"iTunes U is a part of the iTunes Store featuring free lectures, language lessons, audiobooks, and more, that you can enjoy on your iPod, iPhone, Mac or PC. Explore over 100,000 educational audio and video files from top universities, museums and public media organizations from around the world. With iTunes U, there's no end to what or where you can learn."

There is content from American Public Media, Carnegie Mellon, Cornell, Edutopia, Georgia State University, Indianapolis Museum of Art, MIT, Penn State, Stanford, Texas A&M, Vanderbilt, WGBH, Yale, among many others.

Here is a great introductory video to iTunes U.

Did I mention that iTunes U is free?! You will have to download iTunes to your computer. If you are interested in using iTunes U in your classroom and need help getting started, just ask!