The first podcast I would recommend checking out is both engaging and fresh - Grammar Girl. Grammar Girl is a podcast that aims to share knowledge/information on grammar issues - before you write it off as boring, you should know that what makes this podcast exceptional is that listeners interact with "Grammar Girl" by submitting questions/comments which are addressed in her next podcast. This way Grammar Girl is engaging her listeners and building a long term audience.
Another podcast that I personally liked due to the topic was that of iPhone app development course at Stanford University. The drawback about this podcast compared to Grammar Girl is that it is essentially a video recording of a lecture, and there really is no interaction between the podcast listener and the instructor. Also, since these are also video files - the file size is much larger and takes much longer to download.
Podcasts are a great way to publish news and commentary much like a radio broadcast. NPR utilizes podcasts very well to make their programming available beyond the radio audience. There are several great shows such as On the Media, Car Talk, Radiolab which I subscribe to on my iPhone. Like education, NPR's value is in it's content and making that content available through multiple channels (radio, computer, iPod) is important.
