Highly portable multimedia player for various audio and video formats, DVDs, VCDs, and various streaming protocols.

VLC (initially VideoLAN Client) 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.

Full feature list:
http://www.videolan.org/vlc/features.html