This is probably not the best source for podcasts, but I use the Sony software program "MediaGo" (the default program for interfacing my psp3000 with the computer). It is an iTunes-like program with an online store, and there is also a section on podcasts. There are lots to choose from - keeps me happy.
It does have issues auto syncing playlists and podcasts with my psp3000 and Sony Walkman NWZ-S545, but if you like to add content manually to your device it works just fine.
Additionally, beware, movies purchased from the store will not work on your NWZ-s545. Some TV shows work though.
