SciFiPods is a podcast directory specializing in science fiction oriented podcasts.
Warning: The site contains a lot of graphics, and your initial visit to the site will take a long time to render the page. It seems that subsequent visits are faster due to the graphics already being in your browser cache.
The site contains a forum area for podcasters to chat.
You have to be a user of scifipods to post podcast listings. It appears it is free to do so.
This site is part of podcastpickle.com and it's seeming that podcastpickle is realizing a need for niche topic oriented sites. As I browse I keep coming across other topic oriented podcast sites, all created by podcastpickle. I think this is very wise on their part, because generic directories that try to cover the whole world of everything have always left me groping searching for the specific thing I want. The problem is due to the overly generic nature of a directory that tries to cover everything, whereas if your scope is narrowed to a specific topic area then you can focus your indexing to the nature of that topic area.
In SciFiPods.com they have a "genres" list which serves that purpose. Choose a genre, and you're presented a list of podcasts which match.
The site is mildly difficult to navigate.