After talking about a $135 book on Mars, what about something a bit cheaper? How about free? That's pretty much the going rate for podcasts that you can download and listen to on your computer or portable listening device (i.e., iPod). Of course there are podcasts on almost anything you can imagine, and they range in length from a minute or two to multi-hour full radio shows.
There is a growing number of science podcasts, including a great astronomy one I just discovered through iTunes, Astronomy Cast (also available through their own web site). The conversational style and depth of information seem just right - not too technical, but not dumbed-down. I listened to a recent 27 minute podcast on variable stars (#22, February 5, 2007), learned some interesting things, and discovered even more by following the links on their show notes.
Other podcasts: NASA offers a number of "NASAcasts" of various lengths, both audio and video. This Week In Science is an upbeat weekly science review. I just noticed that Phil Plait (The Bad Astromomer) now has a video podcast called Q &BA and I'm downloading the first 30 MB now (need to upgrade my home wireless for faster video!). It's OK - mostly Phil talking to his webcam, but he does add a few visuals in this talk about galaxies. All of these podcasts are available through iTunes, which is pretty much one-stop (free) shopping for podcasts. iTunes itself is free as well and works with your own MP3's, even if you don't have an iPod (you do need to set up an account to download from the iTunes Store, even if you only download free stuff like podcasts). Most podcasts can also be downloaded as MP3 files from their hosting web sites (iTunes is not essential, only convenient).
The only drawback I see to all this is the usual one: time. Time to download the bigger files, and time to listen to them. I guess I can put them on my iPod and go take a walk, but when I do that, I usually prefer music. So I'll probably continue to get most of my space, astronomy, and other science information from reading, but it's cool that the material is out there in audio and video form for those who prefer it that way. There is one podcast that solves the time problem in a sense, 60 Second Science from Scientific American. I suppose science McNuggets are better than no science at all!