Based on my decision to pursue web based media servers I narrowed my Google search criteria and came up with the following candidates:
Wii Media Center X
Written in java by Red Kawa available at http://www.redkawa.com/mediacenters/wiimediacenterx/.
This software is free but is listed as Alpha or Early Alpha and has not been actively developed since Dec 2007.
A service available at www.orb.com which consists of software that you load on your PC which then sends the pictures, music or video to servers at orb which then stream it back to your Wii.
Makes use of the Flash 7 player in Opera on the Wii.
Available from http://tversity.com/. This software allows you to stream pictures, music, videos and Internet content from a PC to your Wii.
An interesting note is that tversity is built from open source but is not open source itself. It is free to home users with an option to upgrade to a Pro version.
Makes use of the Flash 7 player built into the Opera browser on the Wii.
X-oom Media Center for the Wii software costs $40 and is available at http://www.x-oom.com/usa/index.html. It looks to allow access to the following media files: MP3, WMA, OGG, DivX®, Xvid, MPEG2, MPEG4, WMV, JPG, BMP etc.
This project hosted at SourceForge was updated as recently as Dec 2008. It is located at http://wiideocenter.sourceforge.net/wiki/index.php/Main_Page. The software uses mencoder from the mplayer project to encode source media as flash and then download to the Wii utilizing the Opera Flash 7 player.
This project is also hosted at SourceForge but hasn't been updated since Feb 2007 and there has been no activity since Dec 2007.
This is by no means a complete list but rather the software I looked more closely at. Where they existed I looked at the feature sets, looked over the screenshots and read what documentation existing. I even installed it Tversity.
I didn't find any significant endorsements for any of the solutions. The one that looked the most interesting was the orb solution but I didn't really want deal with my content being hosted through someone else's server. In the end I decided to move on.
My next step was to look and see what existed in the way of javascrip/ajax slideshow components that would meet my requirements.