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:

Improved USB mounting and updated channel. Should hopefully help those who are receiving the “Could not find a valid SD or USB device” message
Improved network initialization

http://wiibrew.org/wiki/WiiMC