Podcast Planet is a podcast directory.
It uses a single level hierarchy of topic categories. There are lots of podcasts in the directory, meaning that there are lots of podcasts in each category, which will make it difficult to find a specific podcast.
The show descriptions include a listing of a few episodes. There's a button which launches a popup window that includes a media player.
It's free to add a podcast using the "Suggest a Podcast" link at the top of the page.