After some of Stanford's faculty members offered a few online free course offerings recently (not accredited by Stanford, but you got an unofficial certificate by the instructors), a couple of those instructors have launched a new company by the name of Udacity. Still very new and their business model is still being developed as they are likely to be a for-profit venture.
(Can read more @ Massive Courses, Sans Stanford)
Back to udacity (http://www.udacity.com), currently they are offering 2 free courses.
CS 101: BUILDING A SEARCH ENGINE
Description: This class will give you an introduction to computing. In seven weeks, you will build your own search engine complete with a web crawler and way of ranking popular pages. You will understand some of the key concepts in computer science, and learn how to write your own computer programs. No previous background in programming is expected.
CS 373: PROGRAMMING A ROBOTIC CAR
This class, taught by one of the foremost experts in AI, will teach you basic methods in Artificial Intelligence, including: probabilistic inference, computer vision, machine learning, and planning, all with a focus on robotics. Extensive programming examples and assignments will apply these methods in the context of building self-driving cars. You will get a chance to visit, via video, the leading research labs in the field, and meet the scientists and engineers who are building self-driving cars at Stanford and Google.
Prerequisites: The instructor will assume solid knowledge of programming, all programming will be in Python. Knowledge of probability and linear algebra will be helpful.
You can check out the FAQ for dates and other info. Not affiliated with Google/Stanford.