Everybody knows and loves the VLC player. I prefer it because it plays every video format I can think of and I can set the volume level over 100 %.
To install VLC on Ubuntu 12.10 “Quantal Quetzal” and Linux Mint 14 “Nadia”, do this:
$ sudo add-apt-repository ppa:videolan/stable-daily
$ sudo apt-get update
$ sudo apt-get install vlc