MPlayer-gui

MPlayer is a free and open source media player, available for all major operating systems. It will play all types of free media formats as well as most non-free media formats.

MPlayer2 is a fork of the original MPlayer project, it contains few enhancements.

A GUI is available. To install :

sudo apt-get install mplayer2 mplayer-gui mplayer-skins

Package mplayer-skins contains three different skins, more skins can be downloaded from here.
I downloaded a skin from Deviantart, called simpliX.

Extract the downloaded file ( 7z format ) with Archive Manager. Move the folder simpliX to /usr/share/mplayer/skins :

sudo mv simpliX /usr/share/mplayer/skins

You can also create folder skins in ~/.mplayer and move the folder simpliX over there. ( link ).

Start MPlayer-gui and select your skin and set preferences ( right-click player or screen ) :

MPlayer2 is played from the commandline : http://www.mplayer2.org/docs/mplayer/ .

Example ( playing music from Sky.fm, Smoothjazz ) :
mplayer http://pub8.sky.fm:80/sky_smoothjazz_aacplus

User settings are in ~/.mplayer/config which from the first start contains only one line :

# Write your default config options here!

For settings and options look here :
http://ubuntuforums.org/showthread.php?t=77329
http://everydaylht.com/howtos/multimedia/mplayer/
https://wiki.archlinux.org/index.php/MPlayer#Configuration

Askubuntu/mplayer

Having a Nvidia GT 330 card my config looks like the one from here.

Cool things you can do with mplayer : http://www.linuxandlife.com/2012/07/4-cool-tricks-to-do-with-mplayer.html
http://everydaylht.com/howtos/eyecandy/ascii-movies/

Movie : http://www.sintel.org/download