WiiMC (Wii Media Centre) is an open source media player for the Nintendo Wii. The GUI is powered by libwiigui.

Features:

Ability to play virtually any video or audio format
DVD playback, with DVD menu support (requires IOS 202)
Picture viewer
Music player
Online media support
SD, USB 2.0, SMB, HTTP, and FTP support
Attractive libwiigui-based interface, designed with the Wii in mind

Changes:

Significant changes to improve stability
Significant improvements to video performance
Frame dropping now disabled by default (see Settings)
Corrections to device mounting code (fixes crashes on startup)
Translations to the following languages: Japanese, German, French, Spanish, Italian, Dutch, Chinese (Simplified), Chinese (Traditional), Korean, Romanian, Estonian, and Brazilian Portuguese
Video scaling issues fixed
Audio static bug at EOF fixed
Fixed issues with radio streams
Fixed DVD issues
Improvements to settings loading code
FF/RW time is now configurable
Friendly names now shown for playlists
Radio stream information now shown in the now playing area
Allowed file extensions list expanded
ASS subtitle file support added
Added settings for subtitle language and codepage
Other various bugfixes and improvements

http://wiibrew.org/wiki/WiiMC