The package that you want is ubuntu-restricted-extras. It contains
libdvdcss2 which is the package required to decode commercial DVDs which
have copy protection on them. VLC is a great player, but it won't work with
commercial DVDs unless you have libdivdcss2 installed. The restricted-extras
also enable you to play flash and mp3s and includes ttf-mscorefonts which
makes Windows pages look more natural in Ubuntu.