UC Berkeley Podcasts
Tim Sneath wrote a post on Berkely's CSE podcasts and I have to agree with him on how awesome it is that you can actually listen in on lectures (or even watch them, if you're willing to put up with the Real Media format for the webcasts) given at Berkeley for free.
I'm an Applied Math/Computer Science major here at UCSD, so I know how much these courses cost to actually take. And believe me, the value in them is huge. When I'm in the car, I'm usually either listening to music (on my iPod or my local alt/indie station) or to one of the CS 162: Operating Systems and Systems Programming podcasts. It's been so informative that I've started recommending it to all my friends as well.
Of course, the best part IMO, is that I don't have to take any midterms or finals for these classes. ;)