http://www.xiph.org/ogg/vorbis/
It is a mp3 like encoding / decoding CODEC. Still real early, but seemingly with promise and a dedication to release. It claims to be patent free and open, although the company (xiph) is keeping the codec itself under their control.
Is there growing momentum for it?
I just joined their mailing list.
there has long been a desire among the free software community for a 100% free audio compression format. There have been posts on slashdot that flooded their web servers. Once the docs are complete and they have working sample implementation, I expect it to gain momentum.
It would be nice in the long run for mad or a similar library to also support the vorbis fomat. Now this may be in two years, or maybe longer.