"Several universities are making lectures available as Podcasts. Not every class is work well on an iPod, but the content is much more directed toward people who want to learn and not just be entertained. Of course the flip side of this is that some professors are boring in person, to say nothing of listening to their recordings on an iPod. You may need to look around to find someone who is interesting to listen to, but once you find the right feed, you have a tremendous amount of content regularly published for entire semester.
You can subscribe to a class and set iTunes to download new lectures, sync them with your iPod, automatically delete them once you've listened to them (configured under iPod properties in iTunes). This is a great way to expand your education without spending the time required in a traditional class."
