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
Picture viewer
Music player
Online media support, courtesy of Navi-X
SD, USB 2.0, SMB, HTTP, and FTP support
Attractive libwiigui-based interface, designed with the Wii in mind

Changes:

Synced to MPlayer r31641
Added volume control in Music area
Added option to hide DVD functionality from the UI
UTF-8 SMB support
Ability to use both USB ports (requires updated IOS 202 – WARNING: older versions of IOS 202 are NO LONGER supported)
Increase max SMB shares to 9
Fixed sleep timer
Added “Now Playing” to screensaver
Disable screensaver while slideshow is active
Increased video auto-play limit from 20 to 50
MMS support (thanks denper!)
Improved online stream display (thanks gazstone!)
New SHOUTcast support (WARNING: updating will overwrite your onlinemedia.xml to install new links – backup your old links if necessary)
Audio language setting
Jump to and highlight folder when going up one level
Highlight file when returning to menu
Save settings when power button is used
Added option to use static folder locations
Display parent directory beside Up One Level
Improved restore points behavior
Other miscellaneous improvements/corrections
Language updates

http://www.wiimc.org/