You won't find a better media center than the open-source XBMC, but most people don't have the space or desire to plug a noisy PC into their TV. Instead,
http://lifehacker.com/5391308/build-a-s ... -the-cheap
Build a Silent, Standalone XBMC Media Center On the Cheap
Media PC on Linux
http://polishlinux.org/linux/ubuntu/pc-media-on-linux/
http://polishlinux.org/linux/ubuntu/pc-media-on-linux/
TV Mythos Renewed: MythTV 0.22 with Many Improvements
http://www.ubuntu-user.com/Online/News/ ... provements
http://www.ubuntu-user.com/Online/News/ ... provements