Xcast is the podcasting client (or 'podcatcher,' if you prefer) with a difference. Sure, it does all the normal things like allowing you to subscribe to a feed, download podcasts, watch/listen to them in your favorite app, and organize things with Smart groups. Where Xcast goes above and beyond other podcast clients is the way that it integrates with iTunes. You can easily import your iTunes subscriptions into Xcast, as well as continue to use iTunes' directory structure to keep your files in order. But why are you reading this when you can watch the Xcast screencast and see this app in action.
Xcast is a Universal Binary that is available free of charge (though, as with everything these days, it is a beta) and it requires Tiger.