Free alternative to PowerDVD, WinDVD or any other media player.

Basically, this thing plays almost all formats of audio/video files without requiring additional codecs. 

" VLC media player is a highly portable  multimedia player for various audio and video  formats (MPEG-1, MPEG-2, MPEG-4, DivX, mp3, ogg, ...) as well  as DVDs, VCDs, and various  streaming protocols. It can also be used as a  server to stream in unicast or  multicast in IPv4 or  IPv6 on a high-bandwidth network." 

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