XBMC is a full-featured multimedia center that runs on many current operating systems and platforms. There is currently work underway to get it working on ARM via OpenGL ES2.0. There exists a POC of XBMC running on the BeagleBoard seen here: http://www.youtube.com/watch?v=CYq7f-CrnOc
Optimizations were done as a part of the Google Summer of Code and are described at http://elinux.org/BeagleBoard/GSoC/2010_Projects/XBMC.
An updated version of XBMC on the BeagleBoard-xM can be viewed below.