The University of New South Wales in Australia is running their first year computer science course online for anyone. It's taught by the awesome Richard Buckland and covers C programming, problem solving, machine code and many other topics.
C assignments are submitted online and automatically marked. The next class starts on December 3rd and you can enrol here: https://www.openlearning.com/courses/unsw/computing1
You won't receive any university credit however Richard is a great lecturer and his courses are tons of fun!