free online classes
The Kahn Academy has hundreds of videos on a ton of subjects. These lessons will walk you through everything from ACT prep to Linear Algebra.
Udacity Focusing mainly on computer programming, these classes will teach you to build a search engine, do statistics, program web applications, and more. Complete with tests and instructor interaction.
MIT OpenCourseWare Free classes from MIT. The same ones taught to MIT students. What more could you want?
webcast.berkeley Free classes from UC-Berkeley. The same ones taught to Berkeley students. What more could you want, again?
OpenCulture Aggregating the best in free culture on the internet. Classes, books, movies, and more.