i cannot believe no-one has mentioned VLC
VLC is better than all listed here. its comes wiht its own list of libraries (havent found a file not playable so far) of video and audio streams, can play almost any media (DVD, ISO, etc) in any combination (DVD-nosubmenus, Watch a stream) and you can also stream the media being played onto the network in around 8 different formats....
Quote
Description: multimedia player for all audio and video formats
VLC is the VideoLAN project's media player. It plays MPEG, MPEG2, MPEG4,
DivX, MOV, WMV, QuickTime, mp3, Ogg/Vorbis files, DVDs, VCDs, and multimedia
streams from various network sources.
.
VLC can also be used as a streaming server that duplicates the stream it
reads and multicasts them through the network to other clients, or serves
them through HTTP.
.
VLC has support for on-the-fly transcoding of audio and video formats, either
for broadcasting purposes or for movie format transformations. Support for
most output methods is provided by this package, but features can be added
by installing additional audio plugins (vlc-plugin-esd, vlc-plugin-alsa,
vlc-plugin-arts) or video plugins (vlc-plugin-sdl, vlc-plugin-ggi,
vlc-plugin-glide, vlc-plugin-svgalib). There is also a web browser plugin
in the mozilla-plugin-vlc package.
easy config, many options, cross-platform .... you cant go wrong (windows build is just as good), a must for atleast a last resort