THE best media player available: VLC
 

http://www.videolan.org/vlc/

Plays everything there could possibly be, very stable and cross-platform compatible.

Thumbs up!

Checking it right now

i <3 VLC and Mplayer

VLC plays 99% of the stuff that other player can´t but I don´t like the interface. There are player s with better interfaces and user friendliness.

If stuff won´t play, it´s often a matter of missing some codecs. Google for "g spot codecs" and get the gspot program, it will tell you what codecs you need to install to play a certain file.