Recording audio is not that difficult and posting content to a blog is also not very difficult. To put all the elements together to present your class presentations is daunting. Let's face it, you have better things to do. ProfCast looks to be an elegant solution for taking your class presentation online. It is only for the Mac.
ProfCast - ProfCast - Features: "ProfCast is the ideal tool for recording and publishing your live presentation. All elements of your presentation, including slide timing, animations and voice narration, are recorded. You can then publish your complete presentation on the Web as a Podcast, complete with RSS support."