Audioboo is a very neat service that enables you to make short recordings on your iPhone (and via the web) and then post them. We've tried this out with a couple of 'Boo's already - on our summer reading list, and on a new Simon Mawer novel. The app (and indeed the service itself) is free, and very easy to use (go to Audioboo to download it via iTunes). The 5-minute limit imposes a good discipline, and the recording can be done 'on the hoof', unlike longer and more formal podcasts.
So below, appropriately, is a two-minute description via the Audioboo player, including some quick suggestions on how English teachers might use the service. Thanks to James Michie for the original tip.