The Educational Podcast Network (EBN) is a directory of educational podcasts, aimed at educators. As well as the listing of podcasts, the site hopes to be a source of information about podcasting, explaining what it is and how to get started.
Podutainment (POrtable eDUcational enterTAINMENT) is another directory, this time aimed at actual learners. They are trying to reach a figure of 150 educational podcasters on their site, although the focus seems to be on US education. However, it's an interesting site with a very colourful interface.
The links come courtesy of the Podcast-Education group, which is worth subscribing too. The other podcasting group I belong to is also on Yahoo, Podcasters, is more general, but there is a lot of discussion of what the medium is and what it could be, the technicalities (which microphone to use, etc.), and seem sto be a generous, supportive group.