I absolutely love my new radioSHARK from Griffin Technology. It basically turns your hard drive into a VCR for radio. The USB device records any AM or FM radio broadcast directly to your computer (Mac or PC). The coolest thing is that you can program it to record any program automatically.
Of course, there's already plenty of streaming radio content available online and lots of good shows are archived for listening-on-demand. And you can use tools like Audio Hijack to digitally record them for portability. Even still, radioSHARK is useful for me.
For example, last night my friend Loren Coleman was a guest on Coast To Coast AM, which airs here from 10pm to 3am. I knew I'd be asleep not long after the show came on. (The past 30 days of Coast To Coast are now available online, but you have to subscribe.) So in about 10 seconds, I programmed radioSHARK to turn itself on and record the show while I snoozed. When I woke up this morning, I loaded the audio file into my iPOD and I've been listening to it in my car. I also set radioSHARK to record at the same time each night so Coast To Coast will be waiting for me every morning.
radioSHARK also has a "time shift" feature to "pause" live radio à la Tivo. The one thing that annoys me about the radioSHARK software is that you can only record in AIFF or AAC formats. It's a hassle to convert those big files into manageable MP3s, especially when you're dealing with a several hour broadcast. radioSHARK isn't cheap at $69.99, but it's really easy to use and is sure to provide hours of aural pleasure. Link
UPDATE: BB reader Matt Hamrick says that some people, including himself, have been unable to get radioSHARK to work properly on their Macintosh G5 towers. Ars Technica discusses the problem in their review. Link