Windows/Mac/Linux: Previously mentioned Songbird, the open source, Mozilla-powered, supposedly iTunes-killing media player has updated to 1.4.2, bringing a host of new features, including AAC metadata support, a new feather (skin), CD ripping and support for many mass storage devices.
Apart from the snazzy new purple feather, the biggest features in this release are definitely CD ripping and mass storage syncing (both available as add-ons for 1.4.2 by the Songbird team). The CD ripping tool can look up metadata information on Gracenote (or other services if you prefer, via other add-ons) and can rip songs as FLAC, OGG, or, if you're using Windows, as WMA as well. In addition, Songbird can now sync to more than just iPods — you can now sync any MSC (Mass Storage Class) device, as well as manage firmware on certain devices. Both CD ripping and MSC support, though, currently only available for Windows users — Linux and Mac users will have to wait until at least the next release to test them out.
While Windows users will be very happy to see this feature-filled update, Mac and Linux users will still find Songbird more pleasant to use, especially if migrating from iTunes — 1.4.2 finally allows you to write metadata to WMA and AAC files, meaning all those songs bought or imported in iTunes can have their information edited. However, a bug that still exists in 1.4.2 is that this information will not be transferred back to iTunes for some reason—but don't worry, it's still there in the file.
There are still a host of other bugs in the software (see the release notes for more information), not to mention missing features — but it's definitely one step closer to being the iTunes killer that everyone wants it to be, and despite these bugs, I've found that for the first time, it's usable enough to make a full switch from iTunes — so don't let the bugs scare you away from giving it a test run.
Note that the release notes linked above are labelled as 1.4.1; Songbird was updated again yesterday to 1.4.2 to fix a minor bug with the new feather. In addition, some features are in the 1.3 release notes, even though 1.3 was never released, so be sure to check those too for the full list of new features.
Songbird is free and open source, and is available for Windows XP/Vista, Mac and Linux. Currently, Windows 7 is not supported.