Podcasting has really taken off in the last year or so, and it is a great way to get audio content outside the sometimes stale confines of radio and even internet streams.
Here are some resources:
http://www.apple.com/itunes/
iTunes has a podcasting feature, that lets you both browse and subscribe to podcasts. I haven't used it very much myself, save to stock my girlfriend's iPod, but it is well recommended.
http://juicereceiver...e.net/index.php
Juice is a podcast manager, once you've found things that you like, to download regular shows and organize them.
The Association of Music Podcasting has some good music podcasts, and many science podcasts exist, google on your favorite topic and 'podcast'. Look for the RSS link, to subscribe using the application of your choice.
Attached is my subscriptions file from Juice, in case you are interested.