BOSTON, Massachusetts, USA—Wednesday, May 16, 2007—The Free Software Foundation (FSF) today launched PlayOgg.org, a campaign to encourage use of the patent- and license-free standard Ogg Vorbis as an ethically, legally and technically superior audio alternative to the proprietary MP3 format.
Though the MP3 format has become very common, any time a distributor sells or gives away music encoded as an MP3, they are responsible for paying a fee to the owners of the MP3 patents. These patents are also an issue for developers writing software to work with MP3s. In contrast, the specification for Ogg Vorbis is in the public domain, so anyone can use the format or write software to use it without being dependent on a patent holder for permission.
Full news available from http://www.fsf.org/news/playogg.html
UPDATE: So where do you download music in Ogg Vorbis format?
I recommend http://www.jamendo.com/.