If Firefox and iTunes hooked up, their hatchling could very well be Songbird. Although it's in beta and plenty buggy, it's also a very fun app that's part music player, part Web browser, and all about music discovery, management, and playback.
During installation, it'll ask if you want to load your iTunes music directory or another media directory, or perform the task later. Processing 5,000 songs took about 3 minutes, not a bad pace. It then asks you which of the pre-installed Songbird extensions you want to load. Most of these, like the iPod and USB device manager, only make the app stronger.
The left sidebar provides quick links to bookmarks, downloads, your music library in an iTunes-style interface, and several music discovery Web sites to get your started. When you're looking at any Web site with MP3s available for download, Songbird will open a new window at the bottom main browsing pane. Double-click on a song to play it, while links on the right let you purchase the track from Amazon, iTunes, eMusic, and Amie St. They also tell you the format of the track--MP3 or AAC, for example, and provide a blog link for more info.
Songbird has a growing library of extensions, and support is slowly growing for those written originally for Firefox. Many of the improvements from the last version make for a dramatic change, and Songbird is now stable enough to take flight for the music-loving, Web-surfing fanatic in all of us.