5by5 Radio plays the live stream of 5by5, an online podcast broadcaster, from the menu bar. In addition to playback, it provides an up-to-date schedule of upcoming shows, user notifications when selected shows are live (using Mountain Lion's Notification Center and/or an alert sound), and the option to automatically play these streams when they begin. There are options to automatically launch the app and/or LimeChat 2, the IRC client used by 5by5, at login, and the app's menu contains a variety of links to various parts of the 5by5 website.
Having not been previously exposed to 5by5, I can't vouch for the channel's content; I was unfortunate to tune in during a particularly dull discussion of markdown languages. But the app seems perfectly suited for streaming it, and the many rave reviews on the App Store indicate that the station is not an unpopular one. If you listen regularly, this is not a bad app at all to have around.
Sam's Protip: If you're interested in just a particular show, rather than the whole channel, it may be more efficient to subscribe to the free podcasts for that show available from iTunes. On the other hand, if you're just interested in tuning in to listen casually, iTunes streams the station as well.