Robotics
A couple of years ago I ran into a BBC Click presentation featuring Udacity, the new endavour of the guy who made the DARPA Grand Challange 2005 winning Stanley and later led the development of Google's self driving car, Sebastian Thurn.
These days I think they charge money. But in 2012 most of the courses been free of charge.
Being an engineer I got interested. And taking the course got me kind of hooked to the topic.