Kantaris Media Player can play almost anything you can throw at it - AVI, MPEG, MGEG-AVC, WMV, MOV, MKV, quicktime, matroska, divx, xvid, H264, MP3, WMA, OGG files and more. It can also play DVD's and audio cd's. The player also displays some of the most beautiful music visualizations ever seen. All this is completely free.
It is based on code from Videolan client (VLC) and Bass audio library. The graphical user interface is similar to that of Windows Media Player.