Software Engineering Radio is excellent, I'm learning about all sorts of goings-on within the development community that I'd previously only been aware of in passing. There are something over 100 episodes already, and I've downloaded them all and am working through them. The interviews are particularly interesting, where you get to hear from people like Joe Armstrong, the inventor of Erlang.
IT Conversations is a more eclectic mix of podcasts from many different publishers. I found this through stackoverflow, which is so far a mostly entertaining collection of conversations between Joel (of Joel on Software) and Jeff Atwood regarding their new programming community project. I've also listened to a couple of the Google Developer Podcast and it seems useful for finding out about new Google technologies but the jury is still out on that one.
For the cultural side I've also downloaded some French and Esperanto audio files (not quite podcasts per se) to try to improve my language listening skills. A long time ago I was reasonably capable in French, having studied it in school for five years. Radio France Internationale has a language learning section (langue française) which has various lessons and newscasts in simple French. It claims to be "français facile" (easy French) but apparently that only means limited vocabulary, not limited speed—it's seriously fast. I've got a lot of work to do if I'm going to improve my capability there.
Finally, in my usual style I have rolled my own podcast downloading program. It downloads the RSS feeds, finds new episodes, downloads their associated audio files, queues them up on local hard drive storage, then copies some of them to my MP3 player. I've set it up so it doesn't use more than a configurable amount of space per podcast, so I don't flood myself with 100+ hours of a single podcast. Then, after I listen to an episode I delete it on the player, so next time I run the downloader program it will add more of that podcast. Once I catch up by listening to all the old episodes, it will just copy new stuff as it appears.