With the demise of the Medibuntu repository and libdvdcss not being hosted in the main Ubuntu repos due to licensing issues a new repository is needed from 13.10 upwards. Thanks to the good folks at VideoLAN (makers of the awsome VLC Video Player) there is a ready and updated source available.
wget ftp://ftp.videolan.org/pub/debian/videolan-apt.asc | sudo apt-key add -
echo "deb ftp://ftp.videolan.org/pub/debian/stable ./" | sudo tee /etc/apt/sources.list.d/libdvdcss.list
sudo apt-get update
sudo apt-get install libdvdcss2